APLYSIA. 247 



arising from the internal walls in order to increase the secretory 

 surface. The cells stain deeply. Leaving the chamber on its 

 left side is a short thin- walled duct leading to the winding 

 portion of the mucous gland. The winding portion, as has 

 been already seen, is continuous with the small and large 

 loops of the mucous gland. Both the winding and the loop-like 

 portions stain feebly in contrast to the albumen gland. 

 Parallel septa occur in the looped portion. 



The large hermaphrodite duct leaves the mass on its right 

 side. If the duct be split up longitudinally along its ventral 

 side the connection between the various parts can be traced. 

 The oviducal portion can be followed from the accessory 

 genital mass to the external aperture, but the sperm duct 

 and vaginal duct are best traced backwards from the external 

 aperture. The anterior portion of the large hermaphrodite 

 duct (i.e., the part between the bursa seminalis and the external 

 genital aperture) consists of two chambers (Fig. 20a and 20b), 

 a large one (vag.) into which the penis of the copulating 

 individual is thrust and out of which passes the egg string, 

 and a small portion {int. sem. gr.) partly cut off from the 

 former by paired folds which are continuous with those of the 

 spermatic groove. These are the vaginal or copulatory duct 

 and the spermatic duct respectively. The spermatic groove 

 leaves the genital aperture on its right side, but within the duct 

 it passes dorsalwards and to the left, reaching the latter 

 position posterior to the entrance of the duct of the sperma- 

 theca. The groove becomes less distinct as it is traced back- 

 wards, though its identity is clear in sections owing to the fact 

 that the cells are of greater height and more strongly ciliated 

 than are those of the rest of the duct. The groove is continuous 

 with the channel along one side of the fertilisation chamber 

 (Fig. 20d), and so with the fold that arises in the loop of the 

 little hermaphrodite duct. 



