On Trichodina as an Endoparasite. By T. B. Rosseter. 933 



In my view the species of Trichodina with which I have been 

 dealing differs from T. pediculus, and from any other hitherto known 

 species. 



In particular they have not that hourglass form seen so 

 frequently in T. pediculus, either when found on the tentacles of 

 Hydra, or on the branchia3 of the larva of Triton. They always 

 retain a dome-like form (fig. 2). I do not consider that this 

 persistency of form is due to the sickly condition referred to by 

 other writers in the case of T. pediculus, as all the specimens I have 

 found have been to all appearances in a very healthy state. Again, 

 the number of the denticles exceeds those of T. pediculus; the 

 ring of the acetabulum of the former consisting of thirty, whereas 

 that of T. pediculus has twenty-six. Its endoplast is band-like and 

 curved, and the cuticle offers a greater resistance to the action of 

 acetic acid than the denticles. The pulsations of the contractile 

 vesicle are very sluggish. 



"When the creature is treated with picro-carmine I find that 

 the acetabulum gives way, and the whole of the contents of the 

 interior are ejected, thus leaving the lorica empty (fig. 6). The 

 acetabulum is articulated to the body, and is easily detached by 

 careful manipulation of the compressorium. The greatest length 

 of the body is about 1/500 in., and the diameter 1/400 in. 



I have only to add that when I first found these creatures 

 I thought that possibly they were peculiar to the pond from which 

 I took the newts ; since then I have captured both species of 

 Batrachians in various ponds, within a radius of four miles of 

 Canterbury, and found that they all harboured these parasites, 

 though in none did I find a single specimen of Hydra. The same 

 result followed an examination of a dozen newts sent me by 

 Mr. T. Bolton from Birmingham, the urino-seminiferous organs 

 containing large numbers of the parasites. 



