Now2.))) JICRODEUTOPUS GAYELOTALPA COSTA. 305 
Segmentation. 
A complete account of the cell genesis of the amphipod egg 
has never been published. The segmentation has been followed 
only on the living egg. The most complete account was pub- 
lished by Van Beneden and Bessels in 1869, who carry their 
observations up to the time when the blastoderm begins to 
appear upon the surface of the egg. Other authors merely 
state that the segmentation is total; that the third cleavage 
plane divides the egg unequally; that after the 32-cell stage 
the segmentation becomes irregular; that just before the blasto- 
derm appears on the surface of the egg the difference in size 
between the micromeres and macromeres is lost; and that the 
protoplasm rises to the surface and the cells migrate toward the 
micromere pole to form the blastoderm. In the present work 
the segmentation was followed on the living egg as far as the 
8o-cell stage, and eggs in all stages of development were also 
studied as transparent objects. The drawings were all made 
from stained and cleared eggs, which were afterwards imbedded 
in paraffin, cut as described above, and studied in section. 
I have never seen the process of fertilization in Microdeuto- 
pus, but I have caught many pairs of a closely allied amphi- 
pod in the act of copulation. In these forms the male rests 
upon the dorsum of the female, clasping her with the large 
chelae. He probably assists the female to slough. Some- 
times the sloughing takes place soon after the animals have 
come together, and sometimes I have seen them united for 
days before the female sloughed. Shortly before she sheds 
her shell the male leaves her, and as soon as it is shed he 
returns, and the animals unite in the same way that they did 
before the sloughing took place. They remain together a short 
time and then separate, and shortly after the male has left 
for the second time the eggs are extruded. I do not know 
how nearly the process of fertilization in Microdeutopus agrees 
with what I have observed for the other amphipod, but a 
female of Microdeutopus which had not sloughed, but whose 
eggs were just in a condition to be extruded, was isolated. 
After a time she sloughed, and the eggs were extruded in the 
