KOFOID: DEVELOPMENT OF LIMAX. 81 
F. The Cleavage Cavity. 
l. In Limaa. 
After the blastomeres have reached the widely divergent state seen 
in Plate I. Fig. 14, they begin to flatten against each other, gradually 
losing their individual spherical contour and assuming a hemispherical 
shape. This process occupied, in a case recorded, about an hour, and 
was comparatively more rapid in the latter part. It results in the ap- 
proximate restoration of the egg to the form of a single sphere. The 
superficial region of contact of the two cells appears in the living egg as 
a somewhat irregular line in the now almost obliterated furrow. Very 
soon after this process is completed there appear along this line len- 
ticular or irregular spaces, devoid of the granular structure of the proto- 
plasm, and apparently filled with a clear fluid. Deeper focusing reveals 
the fact that the centre of the apposed faces of the blastomeres is occu- 
pied by a slight cavity, wedge-shaped toward the vegetative pole, and 
broader and rounded toward the animal pole. This cavity gradually 
increases in size, the minor lenticular spaces increase also, and con- 
tiguous ones may be seen to coalesce. Finally, as the central cavity 
increases more and more, and approaches the periphery of the facet of 
contact, the lenticular spaces themselves disappear, probably contributing 
their contents to the encroaching central cavity. The latter now pre- 
sents the form of a broadly lenticular clear space extending from the 
animal to the vegetative pole of the egg, and 
Fieurn E, 
symmetrically developed with reference to these 
poles. The two cells are thus almost com- 
pletely separated from each other by the fluid 
filling the cavity, as will be seen in the accom- 
panying Figure E, giving an optical section 
in the plane of the equator of a two-cell stage 
of Limax agrestis, showing a cleavage cavity. 
They remain in intimate connection, however, 
at the peripheral margin, but this margin of union is in some cases 
reduced to a very thin layer of protoplasm. There is apparently no 
difference in the extent of the union at the two poles. The growth 
of the cavity results in an appreciable increase in the volume of the egg, 
and its contour, as well as that of the cavity itself, is suggestive of the 
high state of tension existing in the egg as a result of this increase in 
volume In extreme cases, as in Plate V. Fig. 34, and in Figure E, the 
VOT. XXVII. — NO. 2, 6 
