296 CKKSSWELL SHEARER. 



stage during which it can live, either internally or externally, 

 on some other host. 



The parasites are able, however, to pass from one host to 

 another without apparent difficulty. This can be readily 

 demonstrated by placing a lobster in a solution of neutral 

 rose in sea-water until the parasites it bears are stained, and 

 then placing it in company with a number of normal unstained 

 lobsters. In the course of a day many of the stained parasites 

 will be found to have gained access to the normal lobsters, 

 while many unstained parasites will be found on the stained 

 lobster. This takes place readily in large tanks where the 

 animals have room to keep well apart. How this passage is 

 accomplished under these conditions I have been unable to 

 observe, as the fenuile lobster is very shy when " in berry," 

 and unsociable, strictly avoiding its mates and companions. 



Both Foettinger and Haswell have drawn attention to the 

 remarkable chitinous jaws with which Histriobdella is 

 furnished. Haswell has made a careful study of these in 

 8tratiodrilus, and has shown how the movements of the 

 component parts of the mechanism are brought about. In 

 Histriobdella the jaws are almost identical, as far as I can 

 determine, with those of Stratiodriius. Foettinger repre- 

 sents them as furnished with many more teeth than I can find 

 to be the case. Their use is not known, as neither Foettinger 

 nor Haswell have made any observations on this head. 

 Unfortunately the intestinal contents are reduced to such a 

 fine amorphous condition as to afford no evidence as to the 

 animal's food. It is probable that the parasites feed on 

 small algfe to a certain extent, as the intestinal contents 

 are usually of a greenish tint. Diatoms occasionally are 

 present, and in some instances would seem to compose the 

 greater portion of the food. This is so in the case of the 

 parasites living on the " berry." In the parasites of the 

 gill-chamber they seem absent, and the intestinal contents 

 consist of a fine brownish mass, among which reddish granules 

 are seen. It is certain that the jaws are not used for tearing 

 the membranes of the lobster's ova as has been supposed. 



