186 CO. CLIFFORD DOBEHLK. 
very well-marked flattening, so that in this region a trans- 
verse section would be elliptical—not circular. This feature 
is so distinctly seen in the living animal, and so characteristic, 
that it is really surprising that it should have escaped notice. 
(Cf. fig. 3.) The animal swims with great rapidity, and 
invariably with the head in advance. 
Gonder was the first to find that a cytostome is sometimes 
present in Chromidina. ‘For the most part one finds 
these Infusoria . . . without any trace at all of a cytostome. 
Only by more exact observation does one notice, in a small 
number, a cleft at the extremity, or at another spot on the 
anterior end.” He “also found Chromidine with a com- 
pletely developed cytostome—though these were, of course, 
less common.” (7%, pp. 246—7.) Now I believe that this 
statement results from the circumstance that Gonder was 
dealing largely with young forms of Chromidina. The 
‘““yudimentary cytostomes” are truly rudimentary in the 
individual, though not in the species. For I have found 
that every large animal possesses a cytostome—and a well 
developed one. As is well known, a Chromidina repro- 
duces by constricting off small portions of itself at the 
posterior end, which then become free, and develop into 
new individuals. Usually these portions are described as 
“buds”; but they are more correctly termed segments— 
being formed, not by budding, but by a process of segmenta- 
tion, like the proglottids of a tape worm. It follows that a 
young Chromidina, just freed from its parent, begins life 
without a mouth. Hence we find all stages in the develop- 
ment of this organella if we examine individuals at different 
periods of growth. (Cf. figs. 4, 5, 6.) ‘he constant presence 
of a mouth in the organism is of importance for understanding 
the nuclear apparatus. 
The vacuoles of Chromidina are non-contractile. 
Nuclear Apparatus.—This is the most important 
feature, regarding which I differ from the other observers. 
{ will first briefly summarise what has already been said 
about it. 
