SOME POINTS IN DEVELOPMENT OF SCORPIO FUI/VIPES. 587

Some Points in the Development of Scorpiofulvipes.

By

Malcolm I<aurle, B.Sc, F.I..S.

With Plate XL.

IN the introduction to my paper on the development ofEuscorpius i ta l icus ('Quart. Journ. Micr. Sci./ vol.xxxi) I mentioned that a species of scorpion (Scorpiofulvipes), which I was permitted to examine by the kind-ness of Professor Lankester, showed a considerable differencein its mode of development from that of Euscorpius. Thisdifference is, as there stated, fundamentally due to the absenceof yolk from the egg of S corpio fulvipes, in which particularit contrasts strongly with that of Euscorpius, in which theproportion of yolk is enormous. Further examination of moreabundant material, which Professor Bourne of Madras collectedand preserved with great care and forwarded to Professor Lan-kester, shows that the specialisation of the embryo in relationto its mode of nutrition has reached a very high pitch.

A few notes with regard to this particular form of Scorpiondevelopment will, it is hoped, be of some service towards anunderstanding of the embryology of Scorpions, and Arthro-poda generally.

Ovary and Ovarian Egg.

The species of Scorpion of which the female reproductiveorgans are described by Duvernoy appears to agree in the pecu-

588 MALCOLM LAURIE.

liarities of those organs with S. fulvipes. Duvernoy, how-ever, deals only with the external appearance of ovaries inwhich the development of the embryo had already advancedsome way.

In Scorpio fulvipes the ovary agrees with that ofEuscorpius in its anatomy, in so far as it consists of a networkof tubes bearing a number of eggs which cause the tubesto bulge at intervals into the body space. Beyond this, how-ever, there are many important differences. The ovarian tubein place of the large oval sessile ova of Euscorpius bears anumber of long diverticula, each of which ends in a solidcoiled appendix (fig. 1). These diverticula were described byDuvernoy1 as the eggs, but the comparatively small egg occu-pies only one tenth of the length of the diverticulum, and liesat its distal end at the root of the appendix (fig. 1, ov.).

The formation of these diverticula can be easily understoodfrom fig. 2, which shows a section of a young egg such as ov'in fig. 1. The egg, which is formed as in Euscorpius by thegrowth of one of the cells of the inner layer of the two-layeredovarian tube, is carried out at the end of an outgrowth of theovarian tube, and is at first completely surrounded by a massof cells of the inner layer. At a stage somewhat later thanthat in fig. 2 an opening is formed through these cells, so thatthe ovum is only separated from the cavity of the diverticulumby the vitelline membrane which surrounds it. There is nospecialisation of any of the cells for the purpose of formingyolk, and in fact the egg is, when ripe, entirely without foodyolk.

The whole diverticulum, as is seen in fig. 1, consists of fourdistinct regions:—A long stalk (st), a thickened collar (c), asomewhat conical portion in which the ovum lies (ov), and along appendix. The stalk is peculiar in that the continuationof the inner layer of the ovarian tube is divided into twodistinct portions. The inner one (fig. 3, i.l.) next the lumen isformed of a single layer of long cylindrical cells with their

1 Duvernoy, " Fragments sur les organes de la Generation de divers ani-maux," ' Mdm. de 1'Acad. Sci. de l'lnstitut,' t. xxiii.

SOME POINTS IN DEVELOPMENT OF SCORPIO FULVIPES. 589

nuclei at various levels, giving at first sight the appearance ofa folding of the walls. The outer portion (fig. 3, i.l'.) is com-posed of a closely packed mass of small cells of which only thenuclei can be made out. Outside this outer portion is the con-tinuation of the outer layer of the ovarian tube (o.L), which con-sists of flattened cells.

In the collar (fig. 4) the two portions of the inner layer areno longer distinguishable. The whole layer, which is enor-mously thickened, consists of clear, highly refracting cells withoval nuclei and well-marked outlines. As development pro-ceeds the collar gradually moves down towards the ovariantube, and as it passes the cells of the diverticulum changetheir form and come to resemble those of the collar. Thischange is preparatory to the active excretion of nutritiousmatter for the nourishment of the embryo in its earlier stages.The greater thickness of the collar is simply the sign of theactivity of the cells within, which require more space in whichto undergo their change in form. When this change isaccomplished the diverticulum returns to its former dimen-sions.

The conical portion above the collar (fig. 1, ov) consists ofthe egg, which when ripe is less than *2 mm. in length (thatof Euscorpius measuring 1'5 mm.), and of the inner layercells surrounding it. This follicle is several cells thick, thecells being the same in appearance as those already describedin the collar. Between the egg and the lumen of the diverti-culum is a small passage, the cells surrounding which are long,and have their nuclei at their outer ends. These threeproximal portions of the diverticulum together reach a lengthof about 2"5 mm.

The coiled appendix, which is longer than all the rest ofthe diverticulum, consists of a solid rod of cells (fig. 5, i.l.)forming a continuation of the inner layer, and is surroundedby the flattened cells which represent the outer layer of theovarian tube (o.l.). The appendix plays an important part inthe nutrition of the embryo, being gradually absorbed asdevelopment proceeds.

590 MALCOLM LAURIE.

The embyro undergoes the whole of its development in thediverticulum, and does not pass into the ovarian tube until it isready to be born.

The development extends over more than six months, myearliest stages having been preserved towards the end ofOctober and the latest in May. How much longer it may takeI cannot say, but the oldest embryos which I have examinedare still some way from being fully developed.

Development of the Embryo.In the earliest stage examined by me the ovum is com-

pletely segmented. The external appearance of the diver-ticulum and appendix is shown in fig. 1, and has beendescribed above. A transverse section (fig. 6) shows theovum, which is about "12 mm. in diameter, to consist of anirregular mass of cells with faintly marked outlines and largeoval nuclei. There appear to be spaces between the cells, butthis may very likely be due to shrinkage. The nuclei for themost part stain very faintly with carmine, and show a slightlygranular structure. Here and there one of the nuclei stainsvery darkly, and such nuclei appear to be undergoing divi-sion. The nuclei are scattered about irregularly, and show notendency to the formation of layers. There is no trace ofyolk either in the cells or in the spaces between them.

In the next stage, between which and the one describedabove there is a considerable gap, various changes have takenplace. The ovum has increased in size to about '15 mm.diameter, though there is considerable individual variation inthis respect, and shows the beginnings of several structures.The cells are chiefly aggregated along one side—the ventral—and towards the posterior end, leaving a space in the middlewhich is full of finely granular substance. This space is wellseen in longitudinal section (fig. 8), and a section in thisdirection also shows very clearly the stomodseum (figs. 7and 8, at.). This structure is a tube, the walls of which areat first one cell thick (fig. 7, st.), and the lumen of whichopens to the exterior of the embryo at the anterior end (i. e.

SOME POINTS IN DEVELOPMENT OF SCORPIO FTJLV1PES. 5 9 1

the end furthest from the ovarian tube), and at the posteriorend into the space in the middle of the embryo describedabove. It is certainly extraordinary that the stomodseumshould be the first structure developed, but the reason will befound in the peculiar mode of nutrition of the embryo in itslater stages.

The outermost layer of the embryo (fig. 7, am.) isseparated from the rest by a distinct space extending allround. It represents the so-called amnion, which is so welldeveloped in Euscorpius, but in this form appears to beconfined to the earlier stages, as I have been unable to findany trace of it in the later ones. A protective envelope ofthis sort is not so necessary in this form, where the embryoremains in situ till it has attained its full growth, as it is ina form like Euscorpius, where the eggs pass into the ovariantube at an early stage, and its slight development and earlydisappearance are probably due to this change of habit in theembryo. Its presence seems to point to the condition inEuscorpius being the more primitive, a conclusion which issupported by many other facts in the development.

In the next stage, in which the embryo has increasedvery considerably in length, the body-wall (fig. 9, ep) isvery thin, and composed of flattened cells on the dorsaland lateral surfaces; while on the ventral surface, wherethe mesoblast and nervous system will afterwards make theirappearance, it is formed of two or three layers of cells withlarge round nuclei.

The gut is not yet formed, but its position is shown by alarge cylindrical mass of yolk, the central portion of whichhas a curiously honeycombed appearance. The rest of thebody space is filled with yolk spheres, the material for theformation of which must have been derived from the cells ofthe diverticulum.

The cavity of the diverticulum beyond the point to whichthe embryo extends is full of a finely granular substancesecreted by the cells which line it. The granular structuremay be due to coagulation of a fluid by alcohol. Here and

592 MALCOLM LAURIE.

there, in the midst of this granular substance, may be seen thenuclei of free cells. These, probably, play some part in thepreparation of the nutritious material for absorption by theembryo, but whether they are derived from the embryo orfrom the walls of the diverticulum, I have not been able toascertain, though I think the latter most probable.

At the posterior end of the body there is a considerablemass of cells, the growth and multiplication of which providefor the rapid increase in length of the embryo. The headend (fig. 10) consists of an almost solid mass of cells, in themiddle of which is seen the laterally-compressed lumen of thestomodseum, which has a highly refractive, probably chiti-nous lining.

At the sides of the stomodseum the cells have become elon-gated (m), and form masses of muscular fibres, extending fromthe stomodseum to the lateral walls of the embryo. A pairof solid outgrowths on the ventral surface represent thechelicerae (fig. 10, I ) .

No traces of the other appendages are present, and it isnoteworthy that this pair of appendages, which in Euscor-pius appears later than the five succeeding pairs, should herebe the first to be formed.

In the next stage only a few points need be noted. Amongthe most curious of these is the formation of a series of dorsalou tg rowths of the body, one to each segment, which give it,when viewed from the dorsal surface, the form shown in fig.11, while in section it has the shape seen in fig. 12. The reasonfor this curious change in the shape of the body is not clear, asthe spaces thus formed are unoccupied by any structures excepta few thin bands of mesoblast. A section (fig. 12) shows thegut completely formed as a tube of large cells surrounding agranular mass of food material. The rest of the body-cavityis occupied only by thin trabeculse of mesoblast except on thedorsal surface, where the mesoblast is present in considerableamount and is hollowed out to form the heart. The yolkspheres, which in an earlier stage occupied the body-cavity, havebeen completely absorbed, and, except for a slight thickening

SOME POINTS IN DEVELOPMENT OP SOORPIO FULVIPES. 593

of the epiblast where the ganglia will be formed, there is notrace of the nervous system in the body. In the cephalicregion the bra in is beginning to form as in Euscorpius bythe proliferation of the cells of a pair of cerebro-opt ic in-vaginations, which are more lateral in position than in the latterspecies, but otherwise completely correspond to them.

At a considerably later stage the gut begins to be constrictedby both circular and longitudinal bands of mesoblast (fig. 13),which divide it into a central tubular portion with a series oflarge diverticula which form the so-called liver. Both the gutand the liver remain full of granular matter, from which thebody-cavity is quite free. The ventral nervous system isby this time completely separated from the epiblast, but as itsformation presents no special points of interest I have not de-scribed it in detail. In the head the stomodseum becomes verychitinous, and is furnished with powerful lateral muscles (fig.14, m). Just opposite the aperture of the stoniodseum is thelower end of the cord of cells which forms the coiled appendixdescribed above (p. 589), and it is by the destruction of this cordof cells that the embryo nourishes itself through all the laterstages of embryonic life. This mode of nutrition, which wasimperfectly described by Duvernoy,1 is very exceptional, and,indeed, more like the nutrition of a young marsupial than any-thing else. The cord is held in position by th,e chelicerse(fig. 14,1), and this is the object of the phenomenally early de-velopment of these appendages as well as of the stomodseum.The comparatively early formation of the gut is due to thesame cause. As might be expected, the chelicerse are con-siderably modified to serve their peculiar function. This isbest seen in the oldest stage in my possession (figs. 15—17),where the chelicerse, apart from their great proportional size,are seen to have the third joint specially developed (fig. 17,I, 3).This third joint is very much larger than the other half of thepincer, and is further provided with a strong band of chitinwhich runs in a somewhat sinuous manner from the base ofthe joint up to the tip. This band of chitin is grooved, and the

1 Loc. cit.VOL. XXXII, PART IV.—NEW SEE. R R

594 MALCOLM LAURIE.

two chelicerse are twisted so that the chitinous plates come intocontact with each other, leaving a small hole (fig. 16, co)through which the cord of cells passes to the mouth. I thinkit is probable that the chelicerae do not merely hold the cordin position, but serve also to crush it. The lower end of thecord consists of horny-looking cell-walls from which all theprotoplasm seems to have disappeared. Whether the embryonourishes itself on the protoplasm of the cells or whether thecell contents are some special substance I have not been ableto find out. It is perhaps worthy of remark that the chitinousplates on the chelicerse are covered in places with a scale-likemarking very similar to that which is so characteristic ofthe fossil Merostomata. The epis tomial lobe (figs. 16 and17, est) is very well developed, and also furnished with chitinous

The five succeeding pairs of appendages closely resembletheir adult state, and need no description here.

The geni ta l opercula are in my latest stage not yet visiblein a surface view, contrasting in this respect with the pectines(fig. 15, vii).

The six metasomatic or caudal segments present one point ofinterest in Sc. fulvipes, namely, that the tail is bent up overthe back, contrasting in this respect with Euscorpius, in whichthe tail lies along the ventral surface.

From what I was able to make out as to the developmentof the median eye, I think that the pigment-cells are epi-blastic. The retina of the eye is formed, as in Euscorpius, froma thickening of the dorsal wall of the cerebro-optic invagina-tion. The thickened portion consists at first of a mass oflarge spherical nuclei, which are distributed through the wholethickness of the retina. In the latest stage which I examined,in which there is already a considerable quantity of pigment,the nuclei are confined to the inner half of the retina, leavingthe outer portion quite clear (fig. 18). The nuclei are, how-ever, no longer all alike; but, while the majority of them retaintheir spherical form, a certain number, forming a band in themiddle of the retina, have assumed an elongated form, These

SOME POINTS IN DEVELOPMENT OP SCOEPIO EULVIPES. 595

latter are the nuclei of the retinal cells, and as from the dis-tribution of the pigment special pigment-cells seem to bepresent, the large spherical nuclei probably belong to theselatter. Absolute confirmation of this view by dissociation ofthe elements of the retina has unfortunately proved impossible,owing to their state of preservation.

Conclusions.

The development of this form adds another to the numeroustypes of development in the Arachnida. It is, as is shownby its mode of nutrition, a highly specialised form. There isno doubt that the type of development represented by E u -scorpius is the more primitive of the two. The chief argu-ments in favour of this view are the formation in Scorpiofulvipes of (1) a rudimentary amnion, and (2) the formationof yolk spheres in the earlier stages, and a mass of yolk roundwhich the gut is formed.

Further, so far as can be made out from the description byKowalewsky and Schulgin,1 the development of Androctonusfollows much the same lines as that of Euscorpius. It iscurious that Euscorpius should resemble the very distantlyrelated Androc tonus so closely, while dififering so markedlyfrom a comparatively near relation like Scorpio; and furtherstudy of the mode of development in other forms would, pro-bably, throw an interesting light on the value of the presentsystem of classification.

The mode of nutrition explains many of the peculiar pointsin the growth of the embryo, everything being sacrificed tothe rapid development of the organs—chelicerse, stomodseum,and gut—necessary for nutrition, and the other appendages,together with the mesoblast and nervous system, being formedat leisure after nutrition is provided for.

I have, unfortunately, not been able to find the remarkablesense organs described by Patten.2

1 ' Biol. Centrlbl.,' vol. vi, p. 525.2 ' Quart. Journ. Micr. Sci.,' vol. xxxi.

596 MALCOLM LATJBIE.

EXPLANATION OF PLATE XL,

Illustrating Mr. Malcolm Laurie's paper on " Some Points inthe Development of Scorpio fulvipes."

Abbreviations.

am. Amnion. ap. Appendix of diverticulum. A. 8. Air-space. Bl. S.Blood-sinus, e. Collar of diverticulum. co. Cord of cells on which embryofeeds, ep. Epiblast. est. Epistome. ht. Heart, hy. Hypoblast. i. I. Innerlayer of ovarian tube. m. Muscles of stomodseum. mts. Mesoblast. n. c.Nerve-cord, o. Central eyes. o'. Lateral eyes. o. I. Outer layer of ovariantube. o. d. Ovarian tube. o. n. Optic nerve, ov. Ovum. r. Nuclei ofretinal cells, s. Stalk of diverticulura. si. Stomodseum. stg. Stigma, v.Vitreous layer, yk. Yolk. The appendages are numbered I, n , HI , &C.For the sake of simplicity the diverticulum round the embryo has not beenfigured, except in Fig. 14.

FIG. 1.—Part of ovary of Scorpio fulvipes, to show the diverticula inwhich the eggs are formed. X f.

FIG. 2.—Longitudinal section of a diverticulum and ovum at an earlyBtage. X *?-.

FIG. 3.—Transverse section of the lower part of a diverticulum. x -4^.FIG. 4.—Transverse section of the swollen " collar" of a diverticulum.

x -V-.FIG. 5.—Transverse section of the solid coiled appendix in which the

diverticulum ends. X -z^-.FIG. 6.—Transverse section of a fully segmented egg. x *-%£.FIG. 7.—Transverse section of front end of a very young embryo, showing

stomodeeum, amnion, &c. X -2-J£.FIG. 8.—Longitudinal section of an embryo slightly older than Fig. 7.

X H*.FIG. 9.—Transverse section. Body of embryo considerably older than

Fig. 8. X H 1 -FIG. 10.—Transverse section through head of same embryo, showing

stomodseum, chelicerse, &c. X if4-FIG. 11.—View of the dorsal surface of an embryo, older than Fig. 9.

SOME POINTS IN DEVELOPMENT OF SCORPIO FULVIPES. 5 9 7

F I G . 12.—Transverse section of body of same embryo. X -^- .

F I Q . 13.—Transverse section of body of an older embryo, x -$£•.

F I G . 14.—Transverse section tbrough head of same embryo, showing modeof nutrition. X -^-.

F I G . 15.—View of ventral surface of advanced embryo. The iii to viappendages have been removed on the left side. X f •

FIG. 16.—View of mouth parts of same embryo, from the front. X f.

F I G . 17.—View of mouth and surrounding appendages of same embryo.The left clielieera has been unfolded to show its structure, and the left chelahas been removed. X J^s..

F I G . 18.—Section through retina of central eye. X ^ & .

***mHuth. Lift' Edm'