Fewkes.] 
32 
[May 16, 
ova were not recognizable. In the brood-sacs of such, instead of 
young Ampliiurae there were found small packets of pink-colored 
ova which, when seen through the wall of the body, impart the red- 
dish color to the aboral body wall. In addition to these packets 
of ova it was likewise found that the brood cavities of many of the 
specimens thus abnormally colored harbored a small Crustacean. 
In an examination of the pinkish clusters of ova in the brood-sac 
of the Amphiura it was discovered that they are in all conditions 
of growth from the first stages of segmentation into a well-formed 
Nauplius. Young Crustaceans free from the packet of ova were 
also found in great numbers in the brood-sacs. These adults were 
identified as belonging to the group of Crustacea called the Cope- 
poda. 
An interpretation of the above facts seems to be that we have 
here a strange instance of parasitism. It is also thought to be 
unique among the Echinoderms. Although many genera of par- 
asitic Copepods are known, I am not familiar with recorded in- 
stances where these parasitic Crustaceans enter the brood-sac of 
an Amphiura and destroy the virility of its host for the good of 
its own offspring. Many instances of Crustacean parasites cas- 
trating other Crustaceans have been recorded by Giard, but in 
these cases it has not been shown that the castration of the host 
is a direct benefit to the offspring of the parasite itself. In Am- 
phiura, however, we have a condition where we can legitimately con- 
clude that the amorphous condition of the ovary of the Amphiura 
is the direct result of the presence of the mother Crustacean in the 
brood cavity of the Amphiura. We may suppose that the parent 
of the Crustacean made her way through the genital slits of the 
Echinoderm into the brood-sacs, and there spayed the Amphiura. 
Packets of the ova were left in the brood-sacs to develop. With 
the destruction of the possibility of offspring in Amphiura within 
her own brood-sacs the future life of the young Crustacea was as- 
sured, and we may readily see, if the precaution of preventing the 
development of young Amphiurse had not been taken, the young 
Crustacean might have fallen easy prey to the vigorously growing 
young of the brittle-star. 
Many questions of theoretical interest suggest themselves in re- 
gard to the curious condition of parasitism mentioned above. How 
by a theory of the advantage which has come to the Crustacean has 
the life within the brood-sac of Amphiura originated ? That it is a 
