CASTLE: NORTH AMEBIC AN KHYNCHOBDELLID^. 59 



VI. PARASITES. 



Three different endo-parasites, of which I find no notice in the litei-a- 

 ture, in addition possibly to one already described by Bolsius ('96), 

 infest more or less commonly the species of Glossiphonia found in the 

 vicinity of Cambridge, Mass. One of these is a small nematode, another 

 a trematode, these two having been observed in the body of G, stagnalis 

 only ; the third is a sporozoon found in at least four of the species 

 described in this paper. 



In January, 1898, I first observed a minute nematode parasite wrig- 

 gling about in the central lacunar space of a live G. stagualis. Another 

 similarly parasitized leech was found upon further search, and a third 

 was found in the following March, the ovary of the host containing at 

 that time full-growia eggs. The parasite in the last-mentioned case lay 

 close to the contractile dorsal blood-vessel, a very common position for 

 it, as subsequent observations showed. In the spring of 1899 several 

 parasitized individuals were collected and studied ; and others were 

 observed in the fall of 1899. 



The length of the parasite is about the same in the case of all 

 individuals examined; namely, 1.43 mm. In form, the worm is slender 

 and thread-like, being widest near the middle of its body, where it 

 measures 0.027 mm. in breadth. From there it tapei's almost imper- 

 ceptibly toward either end. The posterior end of the body is sharply 

 pointed ; the anterior end blunt, its centre being occupied by the very 

 minute, conical mouth. 



Examination of a large number of individuals of G. stagnalis in the 

 spring of 1899 showed that between five and ten per cent of the indi- 

 viduals taken from a particular pond, in which the species abounds, 

 contained the nematode parasite. Usually only a single parasite has 

 been observed in the body of a host, but in one case there were three. 



The nematode is generally found either coiled up (but not encysted) or 

 wriggling about in the central lacuna (body cavity), in the middle or 

 toward the posterior end of the body. The presence of the parasite 

 does not seem seriously to inconvenience its host, for the parasitized, 

 individuals are as large and well developed as those free from parasites, 

 aild contain sexual products in equal abundance. 



Parasitized individuals were kept in aquaria for several weeks without 

 the occuirence of any noticeable change in the condition of the parasites. 

 This fact and the manifest immaturity of all the parasites examined 

 makes me believe that the leech is an intermediate host and that the 



