STOLON FORMATION IN SPECIKS OF TRYPANOSYLLIS. 431 
cusliion of proliferation lias been well estnblished and the 
growth of the stolons themselves lias begun. 
There is no sign in my material of the migration of nerve- 
cells into the stolon from the stock. It is therefore quite 
clear, as Mr. Groodrich has pointed out to me, that these invad- 
ing nerve-fibres form a kind of provisional nervous system 
and must die on the detachment of the stolon and consequent 
separation from the parent cells. But, as is seen later (p. 432), 
as the ectoderm of the stolon differentiates a regular cellular 
Investment of the nerve-cord appears, and the cells composing 
it probably develop nerve-fibres which replace functional]}" 
the original invaders. 
The Further Changes in the Stolon. 
In Pi. 23 bis, fig. 15, is seen a transverse section through a 
stolon of T. gemmipara (VIII), in which the generative 
glands are developing. In fig. 14, a part of the very same 
section, they ivere not to be distinguished from the ventral 
mass of mesoblast between the septa, but now, in all the 
segments already formed in the stolon, a pair of oval glands 
(probably testes) is at present lying almost free in the body 
cavity, but still united by a ventral yoke of mesoblast, 
containing cells of the same character as the glands. 'I’he 
generative cells have large nuclei with conspicuous nucleoli, 
and mitoses are fairly frecjueut. The cells of the peritoneal 
epithelium are rounded and very numerous. Dorsally there 
is only a single layer of cells, but ventrally they are massed 
together, several deep. The fibrous basis of the mesoblast 
{vies, r.), while it formed the undifferentiated core of the 
stolon, still remains as a dorsal mass, from which most of the 
nuclei have migrated, and which is situated between the 
ectoderm and the mesodermal epithelium. 
The musculature is now arranged in four longitudinal 
bands (/. vi.). There are as yet no differentiated muscles in 
the parapodia, Avhich are here developed as merely ecto- 
dermal projections, consisting merely of neuropodium and 
dorsal cirrus. Short acicula have already" appeared. 
