J3L00D-PARASITES OK FISHES OCCUR'RING AT ROVIGNO. 137 



two methods, which, incidentally, may also help to explain 

 this diiference in apparent leugth. The great majority of the 

 individuals on the "wet," iron-hsematoxylin-stained films are 

 in a different position from those on the " dry," Giemsa-stained 

 smears. In the former they are usually found in a twisted S 

 or corksciew-like position (figs. 52-56), while in the latter 

 the parasites are nearly always simply rolled or coiled up to 

 a greater or less extent (figs. 32-37). Now^ in life the 

 trypanosonies are generally observed in a twisted or S-shaped 

 condition, and only rarely, and as it were transiently, in the 

 form of a simple C- We may conclude, also, that death and 

 fixation are at least as instantaneous in the case where the 

 parasites actually come into contact with sublimate and acetic 

 as in the case where the slide is placed in a tube containing 

 osmic vapour. Hence we consider that the position of the 

 parasites on the wet films approximates most nearly, as a 

 rule, to that in which they were the instant before death. 

 What is the cause, then, of the parasites assuming the very 

 different rolled or coiled-up form on " dry " films ? 



The manner of attachment of the undulating membrane to 

 the body has an important bearing upon this question. Figs. 

 52, 53, and 56, from iron-ha3matoxylin slides, show very 

 clearly that in these individuals the undulating membrane 

 was wound spirally round the body at the instant of death. 

 The flagellar border runs now under, now over the general 

 cytoplasm, and in fig. 56 it is seen to run twice under. Are 

 we to regard the membrane as actually attached spirally to 

 the body (when the latter is in a " passive " condition), or as 

 being merely twisted round it at the time by the voluntary 

 contortion of the protoplasm ? We think the latter view 

 affords the true explanation. The appearance of the parasites 

 on Giemsa-stained films gives probably a fairly correct repre- 

 sentation, from a morphological point of view, of the manner 

 of attachment of the membrane — that is to say, it lies along 

 one side of the body, more or less in one plane. The 

 membrane itself, especially on its outer side, is longer than 

 that part of the body to which it is attached. In life the 



