ON THE DEVELOPMENT OF THE SPERMATOZOA. 
81 
ducts, a pair in each (see woodcut). It is suggested to me by 
Professor Lankester that the seminal vesicles possibly originate 
as pocket-like outgrowths of the side-w^alls of these rosettes, 
the anterior pair carrying each an anterior and a posterior out- 
growth, whilst the posterior pair have only each a posterior out- 
growth. The developing sperm-cells shed by the testis are 
collected in the ciliated folds of the corresponding rosettes, and 
in all probability conveyed by their agency to the increasing 
seminal reservoirs. As sexual maturity approaches the three 
primitive pairs of seminal vesicles become larger and larger, and 
finally the four anterior pairs meet in one mass in such a way 
as to form a central body, covering in the rosettes and testes of 
the tenth segment, and also encroaching upon the eleventh seg- 
ment ; to the four corners of this central oblong body are 
attached four lobes corresponding to the anterior and middle 
pairs of the primitive seminal vesicles. A similar coalescence 
of the proximal portion of the posterior pair has taken place in 
the eleventh segment, with invasion of the area of the twelfth 
segment ; but there are only two lobes— the backward-growing 
pair of vesicles which appeared on the septum between segments 
11 and 12. 
The minute structure of the seminal vesicles is remarkable and 
has not hitherto been described. Trom their earliest appearance 
they are essentially highly vascular pouches, but they do not 
exhibit at any time a simple cavity or lumen. The whole of the 
interior of the organ is traversed by vascular trabeculae, which 
consist of excessively delicate connective tissue and exceedingly 
fine blood-vessels. The larger vessels are seen in Plate VI, fig. 
4. The vascular trabeculae form a sort of sustentaculum, in 
which the developing sperm-cells are packed. 
To gain an idea as to the structure of this sustentaculum it is 
a good plan to peel off, wash, and stain a portion of the delicate 
tunic with which the seminal reservoir is covered. On comparing 
this with the sustentaculum seen in sections it is found that they 
agree in essential structure, and, moreover, the inner supporting 
portion is continuous with and formed by the indipping of the 
outer tunic. This outer coat of the reservoir consists of a mem- 
brane supported by fibres irregularly disposed and varying in 
shape. Many of them are spindle-like with a well-stained nucleus 
at the equator, and sometimes branching at the ends (fig 2), 
others are longer sinuous fibres. Among the fibres are seen a 
number of nuclei which, by treatment with nitrate of silver, are 
found to belong to the large flat cells whicli cover the exterior 
of the reservoir, and are similar to the cells elsewhere forming 
coclomic lining of the perivisceral cavity. 
This tunic dips down into the reservoir and forms a Ira- 
VOL. XX, NEW SER, F 
