230 Henry Leste Oszorn, 
modate the egg. I doubt if the eggs remains stationary in passage, 
but think it more likely that they are slowly moved along and 
thrown out of the animal. The number of the eggs is always small; 
there are never more than thirteen present at one time in any of 
the cases that I have recorded, and generally less. In Aspidogaster 
they develop in the uterus to the point where the young worm is 
moving about within the shell and is ready to emerge (VOELTZKOW, 
1888, p. 272). In Cotylogaster occidentalis, according to NICKERSON 
(1900) “the eggs when discharged... contain a fully formed embryo 
with unforked intestine and simple subterminal sucker at the 
posterior end. The body of the embryo is covered in part with a 
simple epithelium bearing distinct tufts of cilia.’ But in C. insignis 
the egg has not undergone the first segmentation by the time it 
leaves the parent. 
Mature worms removed from the mussel and placed in aquaria 
generally soon expel a number of eggs, or can be compelled to do 
so by carefully managed compression. These minute embryos trans- 
ferred by means of a capillary pipette under a simple microscope 
to the center of a slide, were submitted to microscopic examination. 
Fig. 61 is a camera lucida drawing of one of these, and shows its 
condition as it leaves the parent. Eggs were also seen and studied 
in situ both in the living parent and in preserved states, both in 
whole preparations of the parent and in sections. Isolated eggs 
were kept in aquaria from which they were transferred from time 
to time to slides for examination. 
The eggs (Fig. 61) are usually large, measuring in length from 
0.22—0.35 mm, and in width from 0.10—0.16 mm. In Aspidogaster 
(VoELTzKow) they are 0.127 by 0.061 mm, less than half the size 
of C. insignis. They are lemon yellow colored, and of a characteristic 
curved outline. There is a distinct operculum, sometimes one is 
present at each end. By irrigating with acetic acid the contents 
swell and burst off the operculum. The egg cell proper is located 
in the center, surrounded by the yolk cells. It measures 0.04 mm 
in diameter, and has the same appearance in all parts of the uterus. 
In living cells it is invisible, but in section it can be seen and 
identified by its central position, size and structure, it has a distinct 
nucleus, and in some cases two or even four nuclei were seen (see 
Fig. 63), in no case were two such embryo-cells visible in the embryo, 
a conclusive proof that the segmentation does not take place in the 
