420 BULLETIN OF THE 



vesicle. Led by Hertwig's studies on Toxopneustes to a re-examination 

 of this topic, he finds the opportunity, with improved methods of treat- 

 ing the eggs of Phallusia, to correct the statement in the first edition 

 to the effect that the mature eggs are altogether destitute of a nucleus. 

 By employing osmic acid on alcoholic preparations, he is able to demon- 

 strate the existence of a structure (Taf VIII. Figs. 2, 3) which he 

 designates with Hertwig as Eikern. "Dieser Eikern," says Strasburger, 

 *' liegt hier der Hautschicht nicht * an, ist derselben oft sogar angedriickt, 

 ausser dem aber von einer helleren Zone umgeben, die aber nicht scharf 

 gegen das angrenzende Protoplasma abgeschieden ist." I question the 

 accuracy of the conclusion to which Strasburger here arrives. No one 

 has hitherto called attention, I believe, to the possibility of any other 

 interpretation for these figures than that which Strasburger himself 

 gives. Nothing can be further from my purpose than to cast doubt on 

 the persistence of nuclear substance in the egg. It is quite another 

 question if the flattened lens-shaped body represented in Strasburger's 

 figures 2 and 3 (Taf VIII.) is really this remaining nuclear substance. 

 The interpretation which I am inclined to give these figures is quite 

 different, and of some importance as bearing on the existence of polar 

 globules in the Timicata. If, as I have no reason to doubt, Biitschli was 

 right in saying ('76, p. 384) that hitherto nothing had been observed 

 concerning polar globules among Tunicata, this will, in my opinion, be 

 the first evidence tending to show that such bodies are really produced 

 in that group of animals ; for I suspect that these figures represent a 

 stage just prior to the formation of a polar globule. This explanation 

 occurred to me when comparing Fig. 50 (Limax) with Strasburger's fig- 

 ures. Much the most conspicuous part of Fig. 50 is the area! corpuscle 

 {a a') of the peripheral aster. Were the egg for any reason to become 

 less transparent, it is readily conceivable that all the other parts might 

 become indistinguishable and still leave this flattened oval structure 

 visible, and the surrounding radial system would then appear simply as 

 a less granular or clear zone, a condition of affairs, in other words, which 

 is completely realized in Strasburger's figures. The features which make 

 it possible for me to maintain the identity of these two structures may 

 be stated as follows : — 



(1.) The shape of Strasburger's "Eikern." — I know of no case in 



which the egg nucleus (female pronucleus) exhibits such a remarkable 



form, — apparently that of a very much flattened biconvex lens of 



which the thickness is (in Fig. 3) not over one fourth its diameter. 



* This is evidently a typographical error for "dicht." 



