MUSEUM OF COMPARATIVE ZOOLOGY. 393 



tance of fecundation for effecting the changes referred to. Among these 

 may be mentioned A. Miiller ('64), Haeckel (74, pp. 141 -143), and 

 Biitschh ('76, pp. 388, 389), who so recently as 1876 makes this sweep- 

 ing assertion : " Diese Frage nach dem Austritt des Keimblaschens vor 

 oder nach der Befruchtung ist jedenfalls der Miihe werth, naher erortert 

 zu werden, denn es stimmen alle vertrauenswiirdigen Untersuchungen 

 an wirbellosen Thieren darin uberein, dass die Ausstossung erst nach 

 der Befruchtung stattfindet." But with more recent discoveries this 

 question seems to have come nearer a final solution in agreement with 

 Leuckart's conclusion. 



The reviews which follow cover only comparatively recent observations, 

 — principally such as have a bearing on the metamorphosis of the ger- 

 minative vesicle and the formation of the polar globules. 



According to Ratzel und Warschawsky ('69, pp. 548, 549, Taf. XLL 

 Figs. 1,2) the development of the fecundated egg of Lumbricus agricola 

 begins with a change in the germinative vesicle, which surrenders its 

 sharp outline and becomes a "stark lichtbrechender, unregelmassig 

 strahliger Fleck etwas excentrisch gelegen," and with the formation of 

 a narrow, clear streak in the middle of the egg underneath the altered 

 vesicle. This streak subsequently increases in length. Later, both 

 structures disappear. That which entitles these observations to a notice 

 in this connection is the clear streak which remained to the observers 

 of doubtful signification. In my opinion they saw in this streak, how- 

 ever iilcompletely, the maturation spindle in process of formation out of 

 the germinative vesicle. I believe this view is supported by the observed 

 lengthening of the streak, which has so often been seen to take place with 

 the spindle figure. Were it not for the absence of polar globules, which 

 are figured only in later stages {loc. cit, Figs. 3 - 5), I should consider 

 this as probably the first cleavage spindle, since I have seen the same 

 relative position of the pronuclei to the spindle in the case of Limax. 

 The failure to connect this figure, or the germinative vesicle in any way, 

 with the production of polar globules, cannot be surprising, as the 

 authors do not seem to have bestowed any attention on the production 

 of what they, with Rathke, held to be only meaningless, squeezed-out 

 portions of the yolk. 



Those eggs which do not develop retain the germinative vesicle, but 

 its contour becomes less distinct. 



Ratzel ('69, p. 565, Taf. XLII. Fig. 5) saw more than any of his 

 predecessors. He says : In the eggs of Tubifex, which are mature and 

 ready for deposit, the germinative vesicle surrenders its spherical form 



