THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 87 
in figure 36. In giving rise to the spermatosphere the mother cell has become 
swollen and vesicular, the nucleus has disappeared, having probably divided into a 
oreat number of parts, which are, however, not recognisable, and on the surface of the 
swollen vesicle numerous buds have made their appearance. The central part of the 
spermatosphere is to be regarded as the blastophore, and each of the buds on the 
surface as a spermatoblast. 
Figure 388 represents what I take to be three spermatoblasts, or young 
spermatozoa, in a further stage of development, and now separate from the blastophore. 
In the broad end of each a distinct, deeply staining spot, doubtless part of the 
original nucleus, is visible. 
Fieure 39 shows three detached spermatozoa from the testis, obviously derived 
from such forms as those represented in the previous figure, the nucleus forming the 
head, and the protoplasm having greatly stretched out and elongated itself into a 
thin thread to form the tail of the spermatozoon. 
It will be noticed in these fieures that the spermatoblasts seem to separate from 
the blastophore at a very early stage, but it is questionable whether this early 
separation is normal, and may not have been induced by the action of re-agents. 
Moseley figures the blastophores in Bzpaliwm with numerous spermatozoa, of about 
the stage represented in figure 39, still attached, and there are indications, though 
less distinct, of a similar state of things in my sections of Geoplana. 
Moseley observes that in the mature spermatozoa which crowd the vas deferens 
the heads are absent, and states that Max Schultze has observed the same thing in 
other Planarians. In Geoplana spencer, also, the spermatozoa found in the vas deferens 
appear to have no heads. If the head of the spermatozoon, which represents the 
nucleus, be really lost in the fully developed stage, it is, of course, a very remarkable 
circumstance, but that the nucleus should really disappear seems scarcely credible, 
and it is more probable, as Professor Spencer has pointed out to me, that the nucleus 
simply undergoes some change as regards its staining properties. This latter 
hypothesis is supported by the fact that no nuclei are visible in the spermatosphere 
stage shown in figure 37, although they are very distinct in the mother cells and 
appear again very distinctly in the young spermatozoa (spermatoblasts) as shown in 
ficures 38 and 39. 
(0.) The Vasa Deferentia.—These organs differ somewhat strikingly in form and 
position from what Moseley and von Kennel have described in the case of Bipalium, 
Geodesmus and Rhynchodemus. In the two former genera it appears that the vas 
deferens of each side runs close along the inner sides of the testes, which discharge their 
contents directly into it. It hence les just on the outside of the nerve cord. In 
