
Ttc 
TASTE 









PARASITIC HABITS OF CRUSTACEA. 241 
Although many of the Entomostraca, like Cyclops, Cy- 
pris, etc., are active and free swimming little creatures, 
Which swarm in our ditehes and ponds during summer, there 
are a great many forms that are true parasites, and infest 
fishes and other aquatic animals. These are mostly low and 
degraded species, in which the females become enormously 
developed, as compared with the minute males, and take on 
very singular shapes, losing, in many eases, by the progress 
of growth, all resemblance to their original form. In fact 
in some cases when mature they would scarcely be taken 
for Crustacea at all, had not their development been ob- 
served. Among these singular forms are a great number 
of genera which adhere to the external surface of fishes, and 
others to the gills and the membranes of the mouth. Lernea, 
and allied genera, are common upon various: marine fishes. 
Penella, with its long quill-like body, lives on fishes. Cla- 
vella, which has also a very elongated form, lives upon the 
halibut; Trebius and Pandarus infest sharks, ete. ; Caligus 
has numerous species which live on various marine fishes, 
and Argulus is common upon fresh-water fishes, and is also 
found on tadpoles. Prof. Dana, who many years ago care- 
fully studied a species of Caligus* that lives upon the cod, 
states that it does not suck the blood, as had been supposed, 
and thinks that it feeds upon the mucus, as its mouth-parts 
are well adapted for that purpose. But Lernea, Penella, 
and their allies, adhere only by their proboscis, which is 
embedded in the skin, and often barbed with hooks, and 
Probably serves to suck the blood. Some forms of Ento- 
Mostraca allied to these, are internal parasites of serpents. 
A very singular genus called Splanchnotrophus, lives as 
true internal parasites in various naked marine mollusca, on 
the British coasts. 9. brevipes infests Doto coronata and 
olis rufibranchialis, while 8. gracilis is found in Doris 
pilosa and Idalia aspera. Since some of these mollusca 
: inhabit also the coast of New England, we may expect to 

*C. Americanus Dana. American Journal of Science, Vol. 34, p. 225. 
AMER, NATURALIST, VOL. III. 31 
