84 SPIROCILETES. 



dividuals which I have seen no sign of division was dis- 

 coverable. I have, on the other hand, noted the exis- 

 tence of thin forms, which look as if they were formed 

 by longitudinal fission, as was noted by Perrin in Sp. 

 balbianii. Hence the above criterion does not seem 

 adequate for the differentiation of species. Fantham 

 describes Sp. balbianii as occurring in Tapes which 

 points to the probable identity of Sp. tapetos and Sp. 

 balbianii, and throws further doubt on Schellack's 

 classification. The following table embodies the lat- 

 ter's observations (see also Fig. 64) : 



SPIROCH^ETA PINN.E. 



(Gonder, 1908.) 



This organism occurs in Pinna squamosa and P. 

 nobilis. It varies from 10 to 60/1 in length and in 

 breadth from | to 3/x. 1 One end is blunter than the 

 other, and here is situated a blepharoplast. An undu- 

 lating membrane is present. The nucleus may take 

 the form of a single rod or of irregular masses, which 

 are sometimes arranged in groups of four. The rod- 

 form is uncommon and is seen in very motile forms, 

 which Gonder regards as possibly male elements, the 

 irregular masses then characterising female or indiffer- 

 ent forms. A concentration of all the chromatin into 

 one rounded mass was sometimes observed. Such 

 individuals may constitute involution forms. En- 

 cysted forms also occur. 



SPIROCH^ETA MACTR^E. 



(Prowazek, 1910.) 



Found in the crystalline style of the mollusc, Mactra 

 sulcataria (Deshayes), in Japan, this organism is from 

 45 to 70^ in length by 0.8 to i/i in breadth. It has an 

 undulating membrane. 



1 The dimensions of this organism given by Schellack are some- 

 what different (see table above). 



