ox CEISTISPIKA VEXEh'IS NOV. SPEC. 515 



and mode of division of Cristispira veneris — the large 

 '• mollusc spiroclia^^t " Ayliich I found inhabiting the crystal- 

 line style of Venus (Meretrix) casta Chem.in Tamblegam 

 Lake. I shall here give my own observations only — reserving 

 an analysis of my own results and those of other workers for 

 the next section (p. 527). 



( 1 ) Structure. 



Cristispira veneris is one of the largest members of the 

 genus, resembling C. balbianii Certes and C. pectinis 

 Gross. The average length is 50-60 /j., the average breadth — 

 in fixed and stained specimens — about 1"5 fx. A certain amount 

 of variation in the breadth of different individuals is observ- 

 able in fixed and stained organisms — the narrowest being 

 slightly over I fj., the broadest approximately TQ jul. Dried 

 films stained with Giemsa not uncommonly possess a width of 

 almost 2 /n. The longest UTidivided individual which 1 have 

 njeasured was 74 fx in length. 



Living individuals appear to be of approximately the same 

 width, though it is almost impossible to make accurate 

 measurements of them on account of their great motility. 

 The differences in width observable in stained individuals ai'e 

 due, I believe, to the greater or less degree of flattening which 

 takes place in the organisms in making the preparations. It 

 can be seen in the living organisms that they are cylindrical — 

 that is to say, they are circular and not band-like in optical 

 transverse section. In the process of making films, the 

 cylindrical shape is modified by flattening to a band-like 

 shape, thus making the individuals appear broader. Thus, if 

 the diameter of the cylinder constituting the organism were 



22 



1 /a, the circumference wotild be :J- /.i. If complete flattening 



of the cylinder occurred, the breadth of the organism would 



22 

 appear to be i x ^ or approximately 1"6 /{. According to 



the amount of flattening which occurred, different individuals 



