ON THE ANATOMY OF HISTRIOBDELLA HOMARI. 295 



Nothing is known regarding geographical distribution 

 beyond the fact that Histriobdella is common on the 

 lobster of the Channel region. J. P. van Beneden (2), as 

 already mentioned, obtained it at Ostend. He also states in 

 his second paper that he had observed it on the lobster of the 

 Norwegian coast. I have been unable to find it on the 

 lobster at Naples. My observations were, however, limited 

 by the rarity of this animal in the Bay of Naples. I 

 only had the opportunity of examining a few adults. So 

 far it has not been reported as occurring on the American 

 lobster.^ It is remarkable that an animal of such peculiar 

 structure should be represented in Europe by a single species, 

 while its nearest ally should be found in fresh-water streams 

 of Tasmania. 



Little is also known of its life-history and habits. If a 

 small mass of lobster ova with the parasites is placed in a 

 watch-glass of sea-water, it will be noticed that they never 

 crawl on any foreign body brought in contact with them. 

 When left to themselves they collect in groups, twisting their 

 bodies together, and remaining quiet for long periods. On 

 being disturbed they show singular excitement, twisting 

 themselves violently and throwing their heads rapidly from 

 side to side, all the time remaining firmly attached by their 

 powerful hind legs. From time to time they can be seen to 

 bite one another with their strong jaws. 



While the pai-asite can be obtained from the branchial 

 chamber or "berry" of almost any lobster on the coast of 

 England, the manner in which it gains access and passes 

 from one host to another has not been determined. Like 

 most parasites, it has limited powers of locomotion, being 

 unable to swim, and crawling very slowly. It has no larval 

 stage that might assist in its distribution. The eggs are 

 attached in capsules to the lobster ova, and the young 

 undergo their entire development within this capsule, emerg- 

 ing in almost the adult condition. There can be no larval 



' Professor Hen'ick informs me that lie lias never found it on the 

 American lobster. 



