178 
E. A. MINCH IX AND H. M. WOODCOCK. 
aflagellar prolongation is gradually lost, this region of the 
parasite ultimately taking on the short, abrupt appearance 
characteristic of the stout spindles. We certainly have never 
found any indication of such a process, either in the trypano- 
some of the little owl or in T. f rin gillinarum from the 
chaffinch. In those types of form which develop a marked 
aflagellar prolongation, this becomes distinctly more pro- 
minent with the growth of the individual, corresponding with 
the increase in size of the rest of the body. This is the case 
both with the medium-sized, tapering forms (which were 
termed “ definitive ” forms in the first memoir [ 18 ]), and the 
massive “blue” forms, as is clearly shown by a comparison 
of the series of figures, both of the parasite of the owl and 
that of the chaffinch. On the other hand, in the case of both 
the distinct trypanosomes with which these studies have been 
concerned, the stout spindles can be readily connected by 
transitional forms with the small fusiform type (cf. par- 
ticularly the figs. 5, 6, 42-44 of T. fr ingill in arum, which 
show a complete series of intermediate stages). Another 
point to be noted is that the larger individuals of the slender, 
tapering* type have considerably more bulk than the smaller 
individuals of the stout spindle type, and could by no 
possibility become the latter. Zupitza's accouut gives, 
indeed, a somewhat confused idea of the different phases of 
Avian trypanosomes and their relation to one another. This 
is partly due to the fact that he compares trypanosomes from 
quite different hosts as if they were all phases in the life- 
cycle of one and the same parasite, without having regard to 
possible differences in size of the various forms, instead of 
studying the same form in the same host through different 
seasons of the year. 
We have not been able to observe the condition or phase in 
which the trypanosomes occur in the owl in the early autumn, 
not having had any infected birds at this season. Hence, we 
do not know what becomes of the stout spindles, which do 
not pass into the Insectan host. As was discussed in the case 
of T. f ringillinar um, we think it quite likely such forms 
