294 CRESSWELL SHEARER. 



seem a little better developed than those of the " berry/' 

 The parasites are evidently able to migrate rapidly from one 

 situation to the other. On female lobsters whose eggs are 

 about to hatch, many of them have already migrated to the 

 gill-chamber. A certain number, however, are always to be 

 found on tlie old egg-membranes, although the ng^^ have 

 been hatched and the membranes are much discoloured with 

 age, showing that the breeding period had passed some time. 

 I have taken females in this condition, and placed them in 

 tanks with air circulation and kept them under observation. 

 In the course of several weeks the membranes drop o&', but 

 no parasites are found about the tank, showing that they have 

 all taken refuge in the gill-chamber. In the gill-chamber and 

 on the eggs both sexes are present in equal numbers. When 

 the lobster ova are well advanced and about to hatch, the 

 male Histriobdellid would seem to preponderate over 

 the female. On the ova the immature young are found in 

 greater numbers than in the gill-chamber. 



Frequently a large female can be seen carrying a male 

 attached to its back by means of its claspers. These would 

 seem to throw out some sticky secretion, for once the male 

 has taken hold of the female it is unable readily to let go, and 

 gets carried about by the female although it makes violent 

 efforts to free itself. 



In the gill-chambei-, as on the eggs, the parasites show the 

 same tendency to collect in small groups, huddling close 

 together and ci-awling over and over one another. When 

 disturbed they separate, to re-collect shortly in another group. 

 Why they do this is not obvious, as the individuals are some- 

 times all males or immature young, in which the sexual organs 

 have not yet developed. This habit of collecting in groups 

 therefore can hardly be for the purpose of the impregnation 

 of the fenjales. 



I have examined a considerable number of "berried" 

 crabs and rock lobsters, both at l^ljmouth and Naples, 

 without finding Histriobdella. They Avould seem to be 

 exclusively confined to the lobster. 



