APLYSIA. 249 



the tortuous stalk of the spermatocyst. The stalk also com- 

 municates, along the opposite side of the fold, with the base 

 of the large hermaphrodite duct and so with the fertilisation 

 chamber. Sections show that in this region the oviduct 

 and sperm duct are together separated by a complete 

 partition from the copulatory duct, which leads to the sperma- 

 tocyst. The latter, therefore, receives foreign sperm, and. is not 

 a vesicula seminalis in the true sense of the word. The same 

 conclusion follows from an injection of the vaginal duct through 

 the external aperture by means of a glass pipette drawn out to 

 a very fine point. The injection (Prussian blue) ran into the 

 bursa, overflowed into the duct of the spermatheca, reached 

 the stalk of the spermatocyst, and finally entered the fertilisa- 

 tion chamber, whence it arrived at the albumen and mucous 

 glands. By dissecting out the apparatus in a freshly-killed 

 animal before injecting, the order in which the injection mass 

 reached the various portions was ascertained. 



There remains only the oviduct (od.). This, on leaving 

 the mucous gland, passes up along the right side of the 

 large hermaphrodite duct. Its walls are thick, glandular 

 and sacculated, especially during the breeding season. Inter- 

 nally numerous folds project inwards and so increase the 

 glandular surface. The glands probably secrete a fluid which 

 lubricates the passage and so aids in the extrusion of the 

 egg cordon. It has already been noted that the sacculations 

 disappear at the level of the bursa seminalis, and that the 

 anterior portion contains only a vaginal and a spermatic duct. 



The spermatic groove is strongly ciliated. The surface of 

 the penis is covered with a ciliated epithelium, the cilia being 

 longest within the sperm groove. Numerous unicellular 

 glands open on the surface and secrete a lubricating fluid. 

 In some places a depression occurs, and a number of glands 

 open into the crypt so formed. The interior of the penis 

 consists of loose tissue with large blood spaces. By the rapid 



