164 



ROTATORIA 



i)f the T)ody and the insertion of the posterior seta in /■". loii^i^isi-ta. Sloniiuski ( 1926) has 

 shown that in Europe tliis species exhibits a considerable amount of cyclomorphosis and 

 that, in the autumn and winter, forms occur in which the distance Iwtween the posterior end 

 and the insertion of the seta is reduced to 7/*, these forms are called tcniiiuaiis by Slominski 

 who consequently regards the latter as Init a form of longiseta. It is however to be noted 

 that his measurements show that these winter "fcniiinalis" forms are actually shorter and 

 wider than the summer forms in which the insertion of the seta is markedly ventral. It is 



B 



I'^iiiURE 2. — A, Filinia longisela (Ehrenberg), Ootacamund Lake, NS; B, /-'. loiigiscia Togom Tso, 1-49; C, 



F. tcrmwalis (Plate), Ootacamuiul Lake, N 5. 



clear therefore that our form, which we lielieve to be the true Icniiiualis. is a quite different 

 organi.sm to Slominski"s form with a sul)-terminal insertion. 



Our material from Kashmir ( W'ular Lake and the hypi>lininion of L. Manasijalj and 

 from the ice-covered Togom Tso in Indian Tibet has a terminal or sub-terminal insertion 

 (Figure 2 b), while from the Ootacamund Lake the specimens have a typical ventral insertion. 

 Measurements of specimens taken at random from these localities are given in Table I. It 

 will be seen that normally longiseta has a lx>dy al)out twice as long as deep, while in fcniiiiiaiis 

 the body is about two and a half times as long as deep. The material of the former from 

 Togom Tso however is about as proportionately long as fcniiinalis but comparison of the 

 figures of the two forms will show (Figure 2 1), c) that even such elongate specimens of 

 longiseta retain a more giblwus dorsal profile than is found in tenninalis; moreover Slomin- 

 ski's data, as pointed out alx)ve, indicate that elongate forms of longiseta are only found in 

 populations of very large specimens, having a much greater total length than terniinalis, so 

 that they do not constitute a real transition between the two species. On the basis of the 



