0ALIGIDJ3. 
267 
juices of the fish it lives upon. This opinion receives 
confirmation from the observations of Pickering and Dana 
upon the species described by them, as they have never 
detected any blood in the stomachs of those they have 
dissected, though they have frequently opened them im- 
mediately after taking them from the fish. The fluids in 
the intestines were always of a light colour, and they 
conclude that their food must consist of the mucus which 
covers the body of the fish, a secretion which is natural 
to it, and always abundant. 
The Argulus and the Caligi are generally found most 
abundant on weak and diseased fishes. It does not 
follow however, from this, that the fish is rendered weak 
or diseased by the attacks of these parasites, but that 
being previously weakened by wounds or disease, it is 
less able to avoid them, and more incapable of clearing 
itself of them. 
The Caligi change their skin, as well as the other 
Entomostraea, but respecting the process little as yet is 
known. Pickering and Dana, to whom I have so fre- 
quently referred, inform us, that as the time for throwing 
off the old skin approaches, the internal membrane, which 
is destined to form the new envelope, and which may in 
some species be seen through the outer shell, is observed 
to be folded variously into small ridges, over the whole 
body of the animal, which ridges or folds continue to in- 
crease in size as the time for moulting approaches. These 
folds, they remark, evidently result from the animal in- 
creasing in size, within a shell which has become too small 
to admit of its expansion. Nothing seems known with 
regard to their method of copulating. Tilesius, indeed, 
asserts that he has witnessed the act. He says he has 
seen two individuals adhering for days together, the thorax 
of the one fixed to the abdomen of the other. But that 
what he had seen was a true act of copulation is doubtful, 
for he attempts to prove that the Caligus produdus, Mull, 
(which is now ascertained to belong to a different genus 
even), and the curtus , Mull., are the same species, the 
