KOFOID: DEVELOPMENT OF LIMAX. 97 
matter. It is possible that this may represent the segmentation cavity, 
though it does not appear to be present in all cases." This is in a stage 
preceding the formation of the “sixth generation " of micromeres and 
the appearance of the mesoderm. Brooks (78) figures at a late stage a 
cavity in Urosalpinx similar to that found by Bobretsky in a late stage 
of Nassa. Patten ('86) does not figure any segmentation cavity in 
Patella, but in the later stages, before gastrulation, a medium-sized 
central cavity is present. Conklin (791) finds in Crepidula, “at an early 
period, a trace of a segmentation cavity, which, however, is soon 
obliterated.” 
IL Fresh-Water Forms. 
Blochmann ('81) does not discuss the subject ofthe cleavage cavity 
in Neritina, but it is evident from his figures that, if it is present at all 
in the earlier stages, it does not attain a great size, Neritina contains 
a largo amount of yolk, and this may have some effect on the cleavage 
'avity. In the late stages a small cavity appears between the ectoderm 
and the macromeres. 
No mention is made by Sarasin (°82) of a cleavage cavity in Bithynia 
until the close of tho cleavage period. Sections of the early stages were 
not cut. Erlanger (792) finds a large cavity present at the close of seg- 
mentation, i. e. before the formation of the mesoderm and when the 
blastomere contains, according to his estimate, at least sixty cells. In 
Paludina vivipara, Lankester ('76) finds in a late stage of cleavage “a 
central space or cleavage cavity.” A cavity of considerable size is also 
figured by him as present at the time of gastrulation. On the other 
hand, neither Bütschli (77) nor Blochmann (’83) succeeded in finding 
in this species any cavity in the cleavage stages examined by them, nor 
moro than a mere slit-like cavity between the layers at the time of 
gastrulation, Erlanger (91), however, finds a large cavity in tho 
gastrula stage, and it is into this cavity that the mesodermal pocljets 
described by him are evaginated. If Paludina has an ephemeral 
recurrent cavity similar to that of Limax, the apparently discordant 
observations of Lankester, Bütschli, and Dlochmann would be easily 
harmonized. 
I have myself watched the cleavage of the eggs of Amnicola limosa, 
and find that they present a typical recurrent cavity, precisely like that 
of the fresh-water pulmonates. The eggs of Amnicola are enclosed in 
capsules and are surrounded by a jelly-like albumen, They contain a 
small amount of yolk, and cleavage is not so unequal as it is in 
Neritina. 
VOL. XXVII. — NO. 2. 7 
