102 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
structures. No sections of this stage are figured, and the relation of these 
canals to cell boundaries is not determined. The fact that the presence 
of the canals obseures the boundaries between the cells, and that these 
canals are in continuity, suggests the possibility that they may be inter. 
cellular and therefore merely an exaggerated form of the anastomosing 
intercellular spaces so common in Limax. Vejdovsky does not suggest 
their relationship to the cleavage cavity, neither indeed does he regard 
a space found in the two-cell stage as having anything to do with that 
cavity. His grounds for this view, and his explanation of the phenome- 
non, are as follows (p. 105): “Die Hóhle zwischen beiden Furchungs- 
kugeln ist als Ueberrest der Vorgänge zu betrachten, die sich bei der 
Bildung der Zellmembranen beider Furchungskugeln abgespielt haben. 
Diese Höhle zwischen den ersten 2 Furchungskugeln ist bereits oft beo- 
bachtet und als eine primäre Furchungshöhle (!) gedeutet worden. Es 
ist überflüssig eine solche Auffassung zurückzuweisen, einmal, dass es un- 
möglich ist, dass eine Furchungshöhle bereits zwischen zwei ganz gleich 
gestalteten Furchungskugeln zum Vorschein kommen könnte, ein ander- 
esmal, dass derartige Höhle öfters auch während des späteren Furch- 
ungsprocesses zwischen je zwei Kugeln zum Vorschein kommt (vergl. 
Taf. IX. Fig. 11, 14). Gewiss ist diese Erscheinung von den Verhält- 
nissen der Zell- und Kern-platte abhängig.” 
In the absence of the evidence upon which these opinions rest, it 
seems superfluous to discuss them. His suggestion that the formation 
of the cavity of the two-cell stage is dependent upon the phenomena 
of the division resulting in that stage is certainly not sustained by the 
facts. If his opinion were the correct one, we should find a similar 
cavity in the two-cell stages of all forms, fresh-water and marine alike. 
The preceding review of the literature shows that Warneck (50), 
Rabl (79), Fol (80), and Brooks (80) have all noted the recurrent 
character of a cavity in the early stages of cleavage in the Pulmonates, 
but the three later writers have added little to the admirable observa- 
tions of the first named investigator. 
A glance at the summary of the literature on Prosobranch develop- 
ment shows an entire absence of any reference to a recurrent segmen- 
tation cavity in the marine forms, unless an exception be made with 
regard to McMurrich's observations on the cavity in Fulgur. When a 
cleavage cavity does occur, it appears at a very late stage in the seg- 
mentation, is comparatively small, and is never recurrent. ‘The cleavage 
of the fresh-water Prosobranchs has not been fully studied except in 
