MUSEUM OF COMPARATIVE ZOOLOGY. 241 



phenomenon which reappears with each segmentation ; viz. the accumu- 

 lation of a transparent fluid secretion, which becomes periodically evacu- 

 ated into the surrounding albumen (compare pp. 131-136, I. c). 



In this stage there are produced out of this crescent two vesicles 

 whose emergence begins by the protrusion of a small elevation (kleine 

 Erhahenheit) through the protoplasmic envelope of the yolk. The 

 elevation increases, assumes the form of the segment of a sphere, then 

 that of a hemisphere, which gradually becomes a complete sphere rest- 

 ing on a rather stout pedicel. By a constriction of the latter, the 

 sphere appears as a free vesicle. The statement that the second appears 

 gleich after the formation of the first, cannot be taken as exactly rep- 

 resenting the facts. The first globule is larger than the second, and, 

 while the former contains in its clear albuminous fluid small elementary 

 granules, the latter contains a nucleus and nucleolus. Warneck also 

 observed, though very rarely, a third vesicle. The globules do not 

 take part in the formation of the embryo, but continue to exist in a 

 collapsed condition till the young slug escapes from the egg-shell. 



For Warneck these vesicles have not the great importance implied in 

 the name " Richtungsblaschen." The coincidence of the place of their 

 appearance and that of the first traces of segmentation does not establish 

 the dependence of the latter on the former. The views of BischofF, Kol- 

 liker, and Reichert, in referring these vesicles to the germinative vesicle, 

 are especially denied, as far as relates to the snails ; and, as we have 

 already seen (p. 240), their connection with the " clear spot " is denied 

 with equal emphasis ; from all which I believe it clearly follows, as stated 

 above, that Warneck entertained the opinion that a genetic connection 

 did exist between the Purkinjean vesicle and the " clear spot." * 



Warneck's interpretation of the physiological signification of the polar 

 globules hinges on the supposed identity of their formation and detach- 

 ment with the later phenomena of the elimination of a clear liquid. Of 

 the vesicles themselves, he says, they in all probability remove from the 

 yolk an albuminous fluid (p. 123), Of the later phenomenon he says 

 (p. 134), ''Die untauglichen Stoffen werden auch bei dieser Art der 

 Thatigkeit durch Exosmose entfernt." 



From a comparison of the text (p. 125) with the descriptions of the 

 figures (pp. 180, 181) we learn that the elimination of the polar globules 



* P. S. — Again in this point 1 cannot agree with Fol ('79, p. 145) when 

 he cites Warneck in the following connection : " Dans rembranchement des Mol- 

 lusques, la disparition du noyau de I'ovule a ete reconnue par de nombreux observa- 



teurs Je citerai les travaux . . . . de Warneck pour Limnseus et Limax." 



VOL. VI.— NO. 12. 16 



