ON CRISTISPIEA VENERIS NOV. SrEC. 527 



Pen-in — have beau said to occur by several observers, but 

 tlieir statements are based, I believe, upon a wrong iuter- 

 pretation of the facts. This has already been pointed out b}^ 

 Schellack and others, so I will therefore omit further dis- 

 cussion of the matter here. 



The Morphology, Affinities and Classification of 

 Spiroch.ets. 



In the following pages I shall discuss the most important 

 features in the morphology and life-histoiy of the Cristi- 

 spira3, or, as they are commonly called, "mollusc Spirochaits." 

 A discussion of these features is necessary in order to arrive 

 at conclusions regarding the affinities of this remarkable 

 group of organisms, and of Spirochfets in general. 



Two excellent contributions to this subject have recently 

 been made— that of Schellack (1909) and that of Gross (1910). 

 Both these workers employed good cytological methods, and 

 made careful detailed observations on the forms which they 

 investigated. As they have both discussed the earlier work 

 at some length, and entered fully into the literature on the 

 subject, I will confine myself chiell}' to pointing out Avherein 

 my results agree with or differ from those of these two 

 workers. 



The Cell Membi-ane. — The body of a Cristispira is 

 bounded by a cuticle-like covering*, which I shall call the cell 

 membrane. This membrane is usually termed the "peri- 

 plast" — a name originally applied to it by Perrin, who 

 believed the organisms to be Trypanosomes. The use of this 

 special word for the cuticular covering in these tw^o groups of 

 organisms — Spirocha3ts and Tiypanosoines — -appears to have 

 led many people to believe that the cell membranes are so 

 similar to one another, and diiferent from other cell mem- 

 branes, as to indicate affinities between the two groups. The 

 only real similarity between the cell membrane of a Cristi- 

 spira and that of a Trypanosoma is that the same Avord is 

 used for both. Both are, of course, modified forms of mem- 



