J. Johnstone 
399 
then become surrounded by the small indifferent cells so as to appear 
to be enclosed in capsules. The morula-like structures contain one or 
more sustentacular cells at their centres and round these are a 
great number of cells modified so that they come to consist only of the 
chromatic matter of the nucleus. The sperms are developed from these 
small nuclei for we find bundles of them in the later stages of the 
growth of the follicle still adherent to the sustentacular cells. But I 
have not actually seen the growth of the sperms themselves and it is 
possible that there may be other stages. The mature follicles contain 
only the bundles of sperms free or attached to the sustentacular bodies, 
the degenerate capsules and granular debris. The spermatozoa are of 
the usual type, but the heads are extremely small and cannot be resolved 
from the tail portions by a Zeiss apochromatic I'o immersion lens: their 
presence can only be deduced by a rather darker staining, and a blunter 
appearance at one end of the filament. 
The vasa efferentia. These vessels are extremely delicate in 
structure, and as they do not appear to contain the sperms for any great 
length of time it is extremely difficult to trace them in the sections. 
They cannot be made out in stained and cleared preparations, but only 
in sections when several of them happen to lie in the same plane. They 
are very accurately figured by Ldnnberg (1891). They can easily be 
studied in those parts of the proglottis where the typical parenchyma 
has almost entirely disappeared, and where the only structures present 
between the testes are the granular remains of the parenchyma, 
and the dorso-ventral muscle fibres. Their walls are very thin and 
stain with difficulty ; when they are stained well they give the re¬ 
action of ordinaiy connective tissue substance. The wall however is 
a homogeneous layer which is continuous with the outer limiting 
membrane of the testicular follicle, and on its external surface are 
numerous nuclei which have prominent nucleoli and coarsely granular 
chromatic substance : it is remarkable that these nuclei cannot be seen 
on the limiting membrane of the testicular follicles, which never¬ 
theless appear to be developed in the same manner as the walls of the 
vasa efferentia. There are no indications whatever in these structures 
of a wall composed of flattened epithelial cells such as is described by 
Erlanger (1890), while the vessels themselves are so distinct that the 
view of Moniez—that they are only hollowed out cavities in the paren¬ 
chyma (1881)—seems to me to be highly unlikely. In the young 
proglottis the rudiments of the various organs first appear as cords or 
blocks of cells between which is the ground tissue which afterwards 
