BLOOD-PiVRASlTES OF FISHES OCCUBliING AT KOVIGNO. 117 



forms and the large ones of the wide type (fig. 11), but it is 

 not shown clearly in the case of the large forms of the narrow 

 kind, perhaps because the deeply stained cytoplasm of these 

 individuals renders it less apparent. We regard this sheath 

 as probably in the nature of a cytocyst, i.e. an altered layer 

 of the blood-corpuscle. 1 



In describing the structure of the parasites we may begin 

 with the small forms. These show, on the whole, great 

 uniformity in size and appearance. The body is nearly always 

 oval in shape, either a fairly regular oval (figs. 39-42) or slightly 

 pyriforu], the half in which the nucleus lies being in this case 

 somewhat narrower than the other half, and the end less 

 broadly rounded (figs. 2, 8, 16). The average size of these 

 small individuals — the mean being taken of several measure- 

 ments — is4"8yu in length by 2*3 /.t in greatest width on " wet" 

 smears (sublimate-acetic mixtures, iron-h^matoxylin), and 

 4'9^ in length by 2*4 ju in width on " dry ^' smears (osmic, 

 absolute alcohol, Giemsa). We regard the above figures as 

 representing, as nearly as possible, the true or correct average 

 size of this phase. The largest ''normal" dimensions noticed 

 are 5*2 ^u by 2*6/^, and the smallest 4*4 /x by 2*2 ju. We add 

 "normal" because it is interesting and instructive to note 

 one or two instances which well illustrate the considerable 

 variation in this respect, which may be caused solely by the 

 technique. One of them- is afforded by an extremely thin, 

 '• dry " smear in which both corpuscles and parasites are 

 greatly flattened out and consequently enlarged. On this 

 smear the apparent average size of the small form is 5*6^ 

 by 3 ju, and some individuals measure as much as 6'2 /u by 

 3*3^. On the other hand, in a particular "wet" smear 

 (Schaudinn, Twort) both corpuscles and parasites are uni- 

 formly smaller than the normal average on other films made 



^ We have observed nothing so well marked as the capsule, with lines 

 of rupture, described by Sambon and Seligmann, for instance, around 

 certain liajmogregarines of snakes (21). 



- It is, i3erliaj)s, scarcely necessary to mention that tliese cases are 

 not included in the aljove " standard ' 



