KOFOID: DEVELOPMENT OF LIMAX. 91 
division are periods at which the osmotio processes reach a maximum, 
and thus the cleavage cavity may grow rapidly at this time. My obser- 
vations on living eggs show that the period immediately preceding di- 
vision is that of the most rapid growth of the cavity. It is not an 
uncommon thing to find in the later stages neighboring cells in a 
mitotic state enclosing a lentieular space between them. These two 
causes may result in producing in some cases, during the early stages of 
cleavage, an apparent rhythm between the nuclear conditions and the 
periods of expulsion. There is, however, much variation in these early 
stages, and it is impossible to establish in them any such constant 
correlation as Warneck has indicated. 
9. Literature. 
AMPHINEURA, 
No mention is made of any cleavage eavity in the development of 
Dondersia, as described by Pruvot (90). Kowalevsky (83) does not 
discuss the subject in Chiton, but Metcalf (93) describes the cleavage 
cavity as already formed at the four-cell stage. No statement is made 
about its subsequent disappearance. 
LAMELLIBRANCHIATA. 
I. Marine Forms. 
Lovén (48) does not fig 
MA 
gure a segmentation cavity in either Modiolaria 
or Cardium. Barrois (79) makes no reference to any segmentation cavity 
in Mytilus, though his Plate XII. Fig. 16, if it represents a section, shows 
such a cavity. He distinetly states that the segmentation produces a 
body considerably larger than the original ovum. He also notes in the 
two-cell stage the appearance, in one instance, of lenticular refractive 
bodies apparently identical with those figured by Bobretsky as found in 
Nassa mutabilis. These bodies are adjacent to the furrow separating 
the mieromere and macromere of the two-cell stage, and may be due to 
a highly refractive secretion accumulated in these regions. 
Brooks (80°) describes in Ostrea Virginiana a transparent cavity sepa- 
rating the ectoderm from the macromere in dead eggs at a stage when 
the maeromere is almost covered by the very large number of ectoderm 
cells present. He does not regard this space as normal, since the macro- 
mere seems in living eggs to be in contact with the outer layer, and 
there is no indication of a segmentation cavity. It is only concerning a 
later stage, when the macromere has divided into a number of entoderm 
