32 Distribution of the Smaller Crustacea. [Sess. 



is furnished with two divergent barbs, one on each side of 

 the head, so that the head cannot be removed without dissect- 

 ing the eye. The presence of the parasite probably causes 

 the eye to become blind. In illustration of this, on one occa- 

 sion my son tried to catch a sprat — one of a number which had 

 made their way into one of the Leith Docks. This particular 

 sprat had a parasite on one of its eyes, and its would-be captor 

 managed to get his hand almost within touch of the fish on 

 that side on which the parasite was attached, apparently 

 without being noticed, and was about to grasp it, when it 

 turned round, and, seeing him, made off" like a flash of 

 lightning. 



Nicothoii astaci furnishes a most interesting example of 

 limited distribution. This copepod, so frequent on the gills 

 of the common lobster, is apparently found nowhere else, at 

 least in its adult stage ; and it is somewhat strange that, 

 though the parasite is so frequent, there are so few published 

 records of its occurrence. Indeed, I know of no Scottish 

 records of Nicothoii except those I have myself published. I 

 seldom fail to find the parasite on lobsters that have not cast 

 their shells for some time previously. Though comparatively 

 a small species, this parasite is of interest from the two great 

 wing-like lateral expansions of the posterior part of the 

 thorax. These expansions appear to be the result of an 

 extraordinary development of the fourth thoracic segment. 

 The ovisacs are also large, and, with the lateral expansions, 

 give to the species, which otherwise is not unlike some of our 

 common Harpactids, an appearance unusual among copepods. 

 Adult specimens of the parasite are extremely inactive, and if 

 removed from the lobster's gills and placed in sea-water, they 

 make no apparent effort to change their position. The only 

 evidences that they are alive are the peristaltic movement of 

 the intestine and the persistence of their semi-transparent pink- 

 ish colour. Speaking of their sluggishness, Milne-Edwards 

 — quoted by Dr Baird — states that they allowed themselves 

 to be torn to pieces without making the least movement or 

 quitting their hold. But they also seem to be tenacious of 

 life, for ray son removed several specimens from a lobster's 

 gills and placed them in sea-water, where they continued to 

 live for at least five weeks. 



