STOI-ON FORMATION IN SPECIES OP TBYPANOSYLLIS. 429 
In Text-fig. 3 the ventral nerve-cord is shown entering the 
region of proliferation, where it becomes thinner and loses 
the directness of its course, at the same time giving off a 
large and important nerve which runs into the proliferating 
Text-fig. 4. 
Longitudinal section from same series as Text-fig. 3, showing the 
branching of the muscular system. The muscles alone are shown 
in the proliferating cushion and stolons as parallel black lines. 
Lettering as above. X 70. 
lip. Branches from this approach the developing stolon and 
we see one nerve about to penetrate the pedicle of a stolon, 
and this occurs as soon as the segmentation of the mesoblast 
begins. In the last segment of the stock the interrupted 
