50 
Tapeworm from a Parakeet 
unknown cause, none of the specimens contained a well-preserved 
cirrus, so that it is impossible accurately to figure it. Its distal end was 
evidently enlarged into a small thickly nucleated knob, 0-0095 mm. in 
diameter. In the majority of cases this knob was plainly to be seen: 
its junction with the vas deferens however had degenerated into a mere 
strip of structureless tissue. 
Spermatogenesis. 
The testes first appear as small groups of nucleated cells 0-003 mm. in 
diameter, surrounded by a thin but distinct membrane (PL VII, fig. 3). 
There does not appear to be any trace of the endogenous division 
described by von Linstow (4) and Moniez (5); as far as could be ascer¬ 
tained with a magnification of approximately 1500, the divisions were 
amitotic and the products separated almost immediately afterwards. 
This is in accordance with Child’s (1) account. 
After they have reached their full size, the large spherical cells 
(spermagonia) just mentioned become aggregated into groups (Fig. 4). 
The inner side of each cell then elongates, forming a long point directed 
towards the interior of the group, the nucleus of the cell remaining 
in the outer hemispherical portion. A roughly spherical cluster of 
conical cells is thus produced, the inner and narrower ends of the 
cells just touching (Fig. 5). 
Fusion of the cell cytoplasm next occurs at the point of contact 
(Figs. 6 and 7) and continues until all the cells have coalesced to form a 
sphere (cytophore) of varying size, the exterior of which still shows 
traces of its original components in the form of numerous small blisters, 
these being the parts of the cells remaining unabsorbed. Nuclear 
changes, which I have not been able to follow, next occur, resulting 
in a considerable diminution in the size of the nuclei and an increase in 
their number. During this process they remain near the periphery of 
the cytophore (Fig. 8). 
The cytophore now splits internally in such a way as to separate an 
inner sphere (blastophore) from an outer envelope (Fig. 10). Both grow 
rapidly in size. At a certain point the cytoplasm of the outer sphere 
becomes segregated out round the nuclei. These latter now become the 
centres of small separate masses of cytoplasm, each nucleus being 
surrounded by a definite and equal amount. Small uninucleated 
bodies, radially elongated, are thus formed, attached at their narrower 
ends to the still undifferentiated blastophore (Figs. 11, 12). These 
round themselves off into small spheres and, congregating upon the 
