TRYPANOSOMES IN TSETSE-FLIES AND OTHER DIPTERA. 187 
slender in build. From my observations I have come to the 
conclusion that all the different forms may be grouped in three 
classes, the first of which has many subordinate subdivisions. 
I distinguish the three classes recognised by me in the follow- 
ingmanner: (1) Ordinary or multiplicative forms; (2) slender 
forms; (3) Herpetomonas forms. 
(1) The ordinary forms occur in a variety of sizes due 
principally to their growth and multiplication. We may 
distinguish, in the first place, adult or full-grown forms— 
those of the largest size. These are elongated forms, with 
the body more or less cylindrical in build; in some the body 
tapers anteriorly to a fine point (figs. 140, 158, 173, 218, etc.) ; 
in others, on the contrary, the body diminishes in thickness 
very gradually towards the anterior end, up to a point at a 
short distance from the extremity, from, which it narrows 
rapidly to a stumpy point (figs. 138, 139, etc.). We may 
conveniently distinguish these two forms as the serpentine 
and the vermiform respectively ; the free flagellum is short 
in both, but appears longer in the serpentine form, perhaps, 
in some cases, on account of the difficulty in distinguishing 
the exact anterior termination of the body. A third variety 
of the large forms is.the tadpole form, in which the posterior 
end.of the body is swollen out (figs. 142, 221, etc., and 
P. R. §., 878, Pl. XIII, figs. 23, 26); these are the forms 
which I formally identified as females, but I] am now inclined 
to regard them simply as full-grown forms which are about 
to multiply by division. 
The process of division, which will shortly be described in 
detail, leads to a small daughter-individual being split off 
from the larger parent-individual ; in this way young forms 
are produced (fig. 220, etc.)—the smallest individuals of the 
ordinary type. ‘hese young forms are always present, and 
frequently very abundant (Nov. 14th, p. 244). Between them 
and the largest forms every gradation of size is to be found ; 
hence we may safely assume that the small daughter-forms 
produced by division grow up in time into the large forms, 
unless they develop into some other type, as will be described 
presently. 
