364 T. B. ROSSETER ON THE ANATOMY OF BICRANOTJENIA CORONULA. 



stage the spermatozoa are passed down through the vasa efferentia 

 into the vesicula semmaKs, to undergo their final development. 



In its early stage the vesicula seminalis (Fig 5 a c), whose 

 function is the reception and perfecting of the spermatozoa, is 

 a straight tube or canal, a saccular prolongation of the vasa 

 efferentia, in fact, with a small constriction in its centre. It is 

 capable of distension, and is so distended as the spermatozoa 

 accumulate. As development proceeds and it becomes filled 

 with the sperm, the constriction doubles upon itself to form a 

 loop, and thus divides it into tw^o compartments — the distal 

 and proximal sections. The distal portion is bulbous, and in 

 it the spermatozoa are perfected ; the proximal is pyriform, and 

 elongates itself to form the vas-deferens " exterior " (Fig. 5 A d). 

 This is dorsal to, and runs partially over, the receptaculum 

 seminis ; it then bends downwards, sinuously, medio- ventrally, 

 iind, previous to entering the cuTus-pouch, it swells out to form 

 a heart-shaped gland, probably the prostate gland (Fig. 5 A e). 

 That portion of the vas deferens which enters the cirrus-pouch, 

 and for a short distance after it has done so, becomes a stout 

 muscular conduit, the muscles forming themselves into rings. 

 These rings have a diameter of 0'007 mm. At the proximal 

 •end of this pipe it again becomes a sinuous canal, the vas deferens 

 "interior" (Fig. 5 A I). It attaches itself to the cirrus, and, 

 previous to sexual maturity, appears as a sinuous attenuated 

 sac, or elongated vesicle, within the pouch. 



As the spermatozoa within the distal bulbous vesicula seminalis 

 perfect themselves by the development of the head and the 

 shedding of the spermatoblast, they loosen and disintegrate them- 

 selves, and in this condition are passed down the vas deferens 

 " exterior," through the vas deferens " interior " ; into the " sac " 

 within the pouch (Figs. 5 A and 8 k). As the sperm accumulates 

 within, the sac gradually expands, and continues to do so, until 

 by its distension it impinges so closely against the walls of the 

 pouch that it might pardonably be mistaken for the epithelium 

 of that organ. When it is emptied by the act of coition, — there 

 are times when it is only partially emptied, as during the act of 

 coition the sperm secreted continues to flow in by the vas deferens — 

 it again returns to its former state ; and, when once emptied, or 

 even partially so, it is never again refilled. I designate the 

 distal vesicle the vesicula seminalis " superior," and that within 



