82 SPIROCILETES. 



(extremes, 96 and 34^). The short variety tends to 

 be rather thicker than the long. I find, however, 

 spirochaetes differing greatly in length and even more 

 remarkably in thickness, which it would be difficult 

 to sort out into two distinct species. I am inclined to 

 regard the specimens with pointed ends as having re- 

 cently divided. Schellack admits that it is curious that 

 two forms should be found to coexist in each of three 



FIG. 63 . Small spirochaetes from the alimentary canal of Anodonta. 



different molluscs (Anodonta, Tapes, and Ostrea), 

 and there does not seem any good reason for making 

 separate species of these slightly divergent forms at 

 present. On the other hand, without stronger grounds 

 we are not justified in describing them even as sexual 

 forms of the same organism. 



I have found in the alimentary canal of Anodonta 

 minute spirochaetes, 10 to i2// in length (Fig. 63) which 

 may be identical with Sp. hartmanni of Gonder or with 

 Sp. pusilla of Schellack (see below) . 



SPIROCH^TES OF OTHER MOLLUSCS. 



Schellack has examined a large number of different 

 shell-fish and found spirochaetes in many of them, as 

 shown in the following list. He believes that the 

 average measurement of individuals taken just after 

 division is a good criterion of species. He depicts 

 many spirochsetes with a line of separation in the 

 middle of their length, pointing to transverse division. 

 I have not myself been able to observe such specimens 

 in the case of Sp. anodontoz, and even in the longest in- 



