1885. ] On a Parasitic Copepod of the Clam. 123 
No considerable irritation appears to be set up by the presence 
of the parasite in the gill-tubes. The claws of the posterior an- 
tennz and the sete of the various appendages are often invested 
by a yellowish film undoubtedly derived from the blood of the 
host, but no greater exudation resulting in the formation of a 
cyst round the foreign body is to be observed, such as, e. g., sur- 
rounds a Trematode sporocyst in a fresh-water mollusk. The 
granular contents of the intestine of the Copepod havea bluish- 
green tint, which is most readily noticed in the wider rectum, 
but I must leave undecided whether these are derived from the 
blood of the host. 
The development of Myicola appears to resemble that of Lich- 
omolgus closely. When I first collected the parasite in June, the 
eggs were in various stages of development; in August, when I 
was at liberty to study them, the females had lost their egg- 
sacs. 
The difference in form of the male has been already referred 
to; the contrast in locomotion is just as striking ; its movements 
are as rapid as those of a Cyclops. Further investigation must 
show how the females are impregnated. The presence of a well- 
developed posterior maxillipede in the male would appear to in- 
dicate that the female is clasped by these, while the spermato- 
phores are attached to the genital orifice. If such is the case 
this must occur in the suprabranchial chamber before the female 
has become tightly wedged into a gill-tube. 
Whether Myicola will turn out to be associated with Mya aren- 
aria wherever the latter occurs, must be left for the future to de- 
cide. A search for Copepoda in other lamellibranchiates would 
probably yield other interesting forms, although they are hardly 
likely to be of such large size as the species at present described. 
I searched Mytilus and Mesodesma at Metis without detecting 
any such, | ; 
Some idea of the frequency of the copepod may be gathered 
from the circumstance that twenty-five females were obtained 
from fifteen clams out of forty examined! Only one male was 
observed in this gathering, but their small size and comparatively 
free life favor their escaping notice. This observation, further, 
was made in August, when the females had, almost without ex- 
1 Three Malacobdellz were found in the same. 
