182 . E. A. MINCHIN. 
end (fig. 217; see also P. R.S., 8 78, Pl. XII, fig. 6); but in the 
stout forms, when the division has reached a certain stage, 
one of the two daughter-kinetonuclei passes forwards and 
takes up a position between the two daughter-nuclei, thus 
producing a characteristic division-stage (compare HS 54, 59, 
and P. R:S8.; 3°78, Plxdl fig. 12): 
On the seeond day, that is, about forty-eight hours after infec- 
tion, thetrypanosomes are seen to be changing into a type which 
reaches its perfection on the third day, and is best described 
from its later development. What! will call the third-day type 
of trypanosome is of considerable length, appearing under 
forms both slender and stout, but with transitions between 
these two variations (figs. 83-96). The body is generally 
cylindrigal, tapering gradually anteriorly and bluntly rounded 
off posteriorly. ‘The kinetonucleus is round or rod-shaped, 
sometimes large, and generally situated some distance from 
the posterior end. The undulating membrane is not much 
pleated, and the free flagellum is short, even in the more 
slender forms (fig. 86). 
In the preparations of about forty-eight hours we 
find this type sometimes fully perfected, sometimes only 
beginning to make its appearance. In one fly I found in the 
red blood forms similar to those described above as character- 
istic of twenty-four hours after infection (figs. 76, 77), while the 
black blood showed forms more advanced towards the third- 
day type (figs. 73-75). The question at once arises, how does 
this change of type come about? Onaccount of the uniformity 
of structure shown by the third-day type I am inclined to 
derive them all from the stouter type seen at twenty-four 
hours, and to regard the more slender forms seen on the 
third day as derived by divisions from the stouter forms. In 
that case what becomes of the remarkable slender forms seen 
at twenty-four hours? It would be a tempting hypothesis to 
suppose that they have conjugated with the stout forms, and 
that the big forms of forty-eight and seventy-two hours repre- 
sent zygotes, but I am unable to bring forward any facts in 
support of this supposition. If the stout twenty-four-hour 
