ON THE ANATOMY OF HISTKlOBDELliA HOMARI. 293 



in the anterior region, and their course in some instances 

 through more than one segment, seems to preclude any com- 

 parison with Histriobdella.^ Again, in Stratiodrilus 

 the interior feet are retractile, and can be completely drawn 

 into the head. This is not the case in Histriobdella, 

 where the distal joint alone is retractile. The main mass ot 

 the foot is incapable of retraction, even under the action of 

 strong reagents. 'ii 



Histriobdella was found by van Beneden and Foettinger 

 on the eggs of the European lobster, and was considered by 

 them a parasite on these alone. It is, however, like Stratio- 

 drilus, noi-mally an inhabitant of the branchial chamber and 

 gills. It passes to the eggs of the female from the gill- 

 chamber when these happen to be present,- returning to the 

 same situation when the eggs are hatched and the egg-mem- 

 branes shed. In the branchial chamber it is quite diflBcult 

 to detect at first, on account of its almost colourless condition 

 and the fact that in this situation it does not show the excitable 

 movements exhibited while on the eggs, but crawls slowly, 

 keeping close to the mucous membrane. Examination of the 

 branchial surface of the carapace, however, once the eye has 

 become accustomed to distinguishing them, seldom fails to 

 show their presence in this situation in either of the sexes. 

 They prefer the carapace to the gill surface, as it affords 

 a better footing, and the long hairs under which they 

 move prevent their being i-eadily brushed off. To the bases 

 of these they attach their eggs in great numbers, especially 

 towards the margin of the carapace, where the hairs are long 

 and numerous. Comparison of the parasites from the " berry " 

 with those from the chainber shows no difference between 

 them, except that the jaws of the parasites from the chamber 



1 Professor Haswell informs me that since the publication of his 

 account of Stratiodrilus he has re-examined the nephridia and has 

 re-confirmed his statements regarding them. 



- According to Herrick this takes place once in two years. " The 

 Reproductive Period in the Lobster," ' Bull, of U.S. Fish Commission,' 

 vol. xxi, 1901, p. 161. 



