STOLON FOKMATION IN SPECIES OF TRYPANOSYLLIS. 443 
end of tlie stock in successive transverse rows of seven or 
eiglit, the number produced by a single individual being 
between one and two hundred. New rows are established at 
the anterior end pushing those already formed backwards so 
that the oldest stolons are most posterior. Ectoderm and 
mesoderm alone take part in the formation of the stolons so 
that they are without an alimentary canal. Two slightly 
varying types of the phenomenon have been distinguished in 
the two species here studied. 
T. gemmipara, ?T. misakiensis, 
and T. in gens. 
Tlie phenomenon of stolon foi’ina- 
tion here is associated with the 
rapid addition to the stock of a 
tail of forty to fifty segments. 
This develops generative glands, 
like the stolons, hut unlike them, 
contains a direct prolongation of 
the alimentary canal of the 
stock. It seems likely that 
under certain conditions this 
tail may actually develop eyes 
anteriorly and separate off as 
an individual stolon, differing 
from the others only in its com- 
plete alimentary canal. 
The stolons produced have a head 
of the “ Teti-aglene ” type with 
eyes Imt without tentacles or 
palps. The caudal cin-i are well 
develoi^ed and the number of 
segments varies up to thirty. 
T. crosslandi. 
Stolon formation is not accom- 
panied by regeneration of a 
posterior tail (which takes place, 
however, as soon as stolon 
formation is over). But there 
is occasionally at least an incom- 
plete ingrowth from the ventral 
lip of the anus into the dorsal- 
most stolon, which thus forms a 
structure in some degree homo- 
logous with the tail of T. 
gemmipara. 
The stolons have a head with a 
pair of lateral tentacles. The 
caudal cirri are but slightly 
developed, and the number of 
segments is never more than 
eighteen. 
The following divisions coi’respond roughly to the stages 
observed in the growth of stolons. In no example was it 
possible to examine the early formation of the proliferating 
cushion. 
(1) The aggregation of leucocytes in the posterior segments, 
which invade the mesoblast of the proliferating cushion. 
(2) The appearance of centres of proliferation in the epi- 
blast, which cause the formation of stolons. The mesoblast 
VOL. 58, PART 3. — NEW SERIES. 30 
