7uly 5, 1877] 



NA TURE 



179 



that it was round this cell that the true embryo was con- 

 stituted ; but in what manner, each observer appears to 

 have determined for himself. The disappearance of what 

 was accepted as the germinal vesicle was generally agreed 

 to ; but whether before or after impregnation was never 

 fully determined. That it merely retrograded to the 

 centre and determined segmentation as the result of 

 fecundation, was held by many ; while the embryogenic 

 vesicle was said to persist, and from it were derived the now 

 celebrated "globules polaires," or " Richtungsblaschen," 

 which had been variously called by different writers from 

 Carus downwards " white vesicles," '• round vesicles," 

 " clear globules," and so forth, and which are now thought 

 to enter directly into the genital organs of the future being ; 

 Balbiani considering them of much importance in the 

 evolution, inasmuch as they are found ju«t in the region 

 of the ventral layer of the blastoderm where the genital 

 organs appear. 



We have only space for a consideration of one of the 

 instances adduced by Biitschli of earliest ovum develop- 

 ment ; but that may suffice to indicate the distinctive 

 nature of his work. We select the eggs of Nephdis vul- 

 garis. In their youngest state, the yolk is retracted from 

 the delicate membrane, and there is, resting on the yolk^ 

 a minute mound of spermatozoa. At a little distance 

 from this spermatozoal eminence there is an eccentrically 

 placed spindle-shaped body, composed of fine longitu- 

 dinal fibres, which at the equator of the spindle are 

 swollen to a thick shining granular zone. The yolk mass 

 is depressed at one point, and the spindle has its long 

 axis directed to that of the flattened yo'k. At the ends 

 of this body there are clear homogeneous spots, from 

 which rays go forth in all directions through the yolk. 

 This spindle-shaped body Biitschli affirms to be the true 

 germinal veiicle j and it is this which is carried upward 

 to the surface of the yolk, by the elevation of the upper 

 set of rays proceeding from the homogeneous spot over 

 its upper apex, until eventually this spindle is pushed out 

 of the yollc in three segments. In the part first pro- 

 truded fine granules appear, and these retain their con- 

 nection with the fibres in the part still inclosed in the 

 yolk, by fine filaments, which also terminate in a 

 zone of granules. This protruded vesicle is the " Rich- 

 tungsblaschen ;" the real place and relation of which, in 

 the subsequent development of the egg, is nowhere deter- 

 mined by these researches. In the stage of partial pro- 

 trusion of this vesicle, at about a quadrant from the 

 point of its exit, another clear space arises sending out 

 its radial rays ; this enlarges, moves to the centre, and 

 the germinal vesicle — now the " Richtungsblaschen " — is 

 at this time quite protruded. At a point in the yolk deter- 

 mined by the point of exit of the " Richtungsblaschen," 

 two minute nuclei appear, one in the upper margin of the 

 clear space, and the other between that and the point of 

 exit of the said vesicle. They are at first entirely dis- 

 connected, and both, by treatment with acetic acid, prove 

 to be true nuclei. But they soon unite in the clear spot 

 or space, and, at its expense, rapidly grow. They become 

 a perfect nucleus with a distinct envelope and fluid con- 

 tents, and distributed within the latter'are dark granules. 

 While these processes have been taking place two of the 

 three segments of the " Richtungsblaschen " have again 

 united, and at the same time the transformation of the 



nucleus begins. At two points on opposite sides of the 

 nucleus, and in the direction of the long axis of the yolk, 

 there arise clear spots and their accompanying rays. 

 Between these, the nucleus differentiates itself into long 

 fibres, and becomes a spindle-shaped body exactly like the 

 germinal vesicle. An equatorial zone arises in it which 

 is called a nuclear-band (kernplatte), which now divides; 

 and each half recedes to the opposite ends of the spindle- 

 like body. These ends now lose their points and become 

 rounded, and in the mean time occurs the furrowing or 

 constriction of the yolk. Another equatorial band arises 

 in the nucleus or spindle, and when the constriction of 

 the yolk is half accomplished the formation of nuclei of 

 the second generation takes place from the ends of the 

 spindle, these being nuclei in the completest sense. These 

 fuse together and grow at the expense of the clear space — 

 the growth of the nuclei and the diminution of these 

 homogeneous spaces being in all cases correlative. When 

 these nuclei are developed both hemispheres of the 

 yolk collapse, and an almost spherical shape is again 

 resumed. 



What became of the fibres of the spindle was never 

 discovered, but'about this time the remaining segments of 

 the " Richtungsblaschen " reunite, and in it a system of 

 fibres appears. The following fission processes are but 

 repetitions of this. 



It becomes from the above apparent that Biitschli takes 

 it for granted, first, that the eggs studied had been subject 

 to no earlier developmental changes than those with which 

 he starts. Next, that there can be no question as to the 

 identity of his "spindle-formed body" and the germinal 

 vesicle. He further at first claimed the extrusion of this 

 germinal vesicle as the " Richtungsblaschen,," as a sole 

 result of the stimulus of impregnation ; and ventures to 

 consider that the process,of nucleus formation described 

 is widely diffused in the animal world, and that it is 

 probably universal in impregnated eggs. 



But (i) there is not the remotest evidence to show that 

 processes of considerable import m.ay not have preceded 

 the condition with which these investigations started ; 

 complex processes are still known to occur in the unim- 

 pregnated ovum. We have only indeed to turn to the 

 next example given by Biitschli himself to prove all this. 

 In Ciiculanusclegans the ovum leaves the ovarium without 

 an envelope ; and within the yolk is seen the "large round 

 germinal vesicle and the germinal spot." The latter 

 vanishes after impregnation, and the germinal vesicle 

 becomes eccentric — and the next'thingwe are told is that 

 "the germinal vesicle was no longer in the yolk, but 

 instead of it there was a spindle-shaped something like 

 that seen in Nephelis." How was the change effected ? 

 What were the steps ? The transition is all-important, 

 but how it happened is not worked out ; and it would be, 

 in so important a question, a matter of the greatest in- 

 terest to know lioi^i the perfect spindle-formed body, with 

 which these observations begin, arose. Nothing final 

 can issue in this inquiry until, from first to last, every 

 process and every step therein has been consecutively 

 made out. 



(2) The identity of this body with what is known as the 

 germinal vesicle is certainly probable, but by no means 

 certain, at present. It is certainly true that this supposi- 

 tion derives considerable support from the fact that Ratzel 



