CALIGlDiE. 267 



juices of the fish it Hves 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 

 Entomostraca, 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 Caligm productus, Miill. 

 (which is now ascertained to belong to a different genus 

 even), and the curtus, Miill., are the same species, the 



