QUEKETT MICROSCOPICAL CLUB. 545 



series of the Journ. Q. M. C. Mr. Grundy exhibited a slide of 

 mounted copper which illustrated the same lighting. 



Mr. J. Wilson read some notes by Mr. H. Whitehead, B.Sc., 

 F.R.M.S., on an epizoic infusorian, Trichodina Steinii C. and L., 

 found on Turbellaria. These were found on a specimen of 

 Mesastoma tetragonum, moving about over the surface of the 

 body and between the folds. They are a species closely allied to 

 Trichodina pediculus, which is frequently found on Hydra, but 

 differs in that T. pediculus has an inner as well as an outer ring 

 of teeth. The body of T. Steinii varies considerably in shape; 

 but when at rest it is cylindrical, the diameter at the base being 

 equal to the height (about 40 /a.), the basal circle of cilia being in 

 contact with the body of the Turbellarian, while the adoral cilia 

 form a spiral leading to the mouth. When free-swimming, the 

 adoral cilia are retracted, while the basal circlet is used for 

 the purpose of locomotion. The protoplasm contains a number 

 of small spherular structures, and one or two contractile vacuoles 

 are to be seen. It possesses a large horseshoe-shaped nucleus, 

 which can only be seen in stained specimens. Mr. Whitehead 

 pointed out an important discrepancy which appears between 

 Saville Kent's description (probably taken from Claparede and 

 Lachmann) and his own observations. Saville Kent stated that 

 the posterior horny ring was continuous and denticulate only on 

 its outer edge. A careful examination of the adherent organ 

 shows it to consist of an outer circle of cilia, and within this 

 a circle composed of about eighteen or twenty separate chitinous 

 teeth, with the points directed obliquely outwards. Vejdovsky, 

 in 1881, published a detailed account of the species, and stated 

 that he had found T. Steinii on Planaria gonocephala. As far as 

 can be seen, the host suffers no inconvenience from the trichodina, 

 and there is no evidence of parasitism ; consequently the non- 

 committal term " epizoic " is more satisfactory than " parasitic " 

 in this case. 



A discussion followed, during which Mr. Rousselet said he 

 remembered, many years ago, finding a T. Steinii on a rotifer. 



In reply to a question by Mr. Scourfield about the formation 

 of chitinous teeth, the chairman stated that some stalked, 

 non -contractile forms of Vorticella fasten themselves down by 

 means of a kind of glue exuded by the cilia, which hardens. 

 Probably these teeth are an adaptation of similar development. 



