382 



PROF. W. J. DAKIN ON THE 



crowded condition of tlie body-cavity. It is difficult to separate 

 the delicate ducts in preserved and consequently hardened spe- 

 cimens. The seminal vesicle may, however, attain such a size 

 at a certain season of the year (September-October) as to fill up 

 most of tlie body-cavity where it occurs. This is well shown in 

 the illustration PI. III. fig. 4, which is a photomicrograph of a 

 transverse section passing through such a seminal vesicle. The 

 wall of the seminal vesicle is rather delicate, being formed of 

 somewhat flattened epithelial cells (PI. TV. fig. 13). The vas 

 deferens leaves tlie seminal vesicle at the opposite side from the 

 entrance ot the testis or testis duct. (It is impossible to divide 

 that portion of the reproductive organs beyond the seminal vesicle 

 into regions.) 



The first portion of the vas deferens following the seminal 

 vesicle is lined by almost cubical cells (PL lY. figs. 13, 15). 

 This leads imperceptibly into a section (by far the longest) the 

 wall of which is of flattened cells, the epithelial layer being, how- 

 ever, supported by a la.yer of longitudinal and circular muscle 

 fibres. This section of the vas deferens coils about, entangled 

 with its fellow of the opposite side and also with the terminal 

 portions of the accessory reproductive glands. 



What we may term the vas deferens of the right side con- 

 tinues its course to the left of the alimentary canal right away 

 on towards the posterior extremity of the animal (see PI. I. 

 fig. 3, Vas.def.r.). Just in front of the male opening it dives 

 under everything, even the two nerve cords, and, reaching the 

 right side, it continues its way anteriorly again. 



This extraordinary difference from the course of the other vas 

 deferens (PI. I. fig. 3, Yas.def.l.) is always met with. It was 

 indicated by Bouvier, but his drawing is not quite accurate. 



Eventually, somewhere about the 4th or 5t]i leg from the pos- 

 terior extremity, both vasa, deferentia join up to form a very wide 

 terminal unpaiied tube. The first portion of this wide duct has 

 thin walls, the epithelium consisting of flattened cells (PI. IV. 

 fig. 16). As the reproductive aperture is reached the walls become 

 thicker (PI. V. -fig. 17) owing to a gradual development of trans- 

 verse and longitudinal muscles. The tei-minal portion (PI. Y. 

 fig. 18) is very muscular, the walls being quite thick. It is 

 probably extrusible. This last section turns over to the right 

 side of the alimentar}^ canal and passing underneath the right 

 nerve-cord reaches its opening to the exterior (see PI. I. fig. 3). 



As Bouvier pointed out, the vast chamber formed by the 

 commencement of the unpaired duct is usually filled with a mass 

 of spermatozoa, the whole taking the form of a convoluted cord 

 (PI. IV. fig. 16, 8p.). There is no sign of any chitinous envelope. 

 It will be seen that the unpaired section of the reproductive 

 ducts formed by the union of the two vasa deferentia is the region 

 for the storage of spermatozoa and their massing into spermato- 

 phores — not the so-called seminal vesicle, where spermatogenesis 

 takes place. 



