APLYSIA. 201 



attachment of the ctenidium. It is a small slit- like aperture, 

 and can be found by gently stroking the surface in this region 

 with the handle of a scalpel. 



Glands of the P allied Cavity. Two sets of glands, both 

 probably defensive in function, open into the pallial cavity. 

 These are the purple gland and the opaline gland. 



The purple gland (Fig. 7, p. gl.) is situated on the under 

 side of the free edge of the mantle shelf and occupies a clearly 

 defined area. In the resting condition it is yellowish or brown 

 in colour. The numerous ducts of the large unicellular glands 

 give a pitted appearance to this region. If a living Aplysia 

 be irritated by forcibly holding up the mantle skirt or by 

 removing the animal from sea-water, a rich, reddish purple 

 dye mixed with abundant mucus issues from the mantle glands. 

 The discharge is not instantaneous, but takes place within a 

 few seconds. The dye mixes very slowly with the sea- water 

 and forms an effective screen under cover of which the soft- 

 bodied and otherwise helpless Mollusc can escape from its 

 foes. 



The Opaline Gland (Vayssiere), Poison Gland (Cunning- 

 ham), Grape-shaped Gland (Cuvier), Gland of Bohadsch 

 (Mazzarelli) lies beneath the floor of the anterior part of the 

 pallial cavity, into which it discharges by numerous apertures, 

 which tend to fuse in small groups in some individuals 

 (Fig. 7, op. gl.). In well preserved specimens the orifices may 

 be rendered visible by stroking the surface with the handle 

 of a scalpel. In the largest of the European species, Aplysia 

 limacina, the ductlets unite and discharge through a single 

 external aperture, and in this species, too, the gland has the 

 appearance of a bunch of grapes. Cuvier 's name, grape- 

 shaped gland, is applicable therefore to this species only. 



[Reflect the parapodia, insert scissors into the circular 

 aperture in the mantle on the summit of the visceral dome, 

 and make radial cuts towards the edge of the mantle, thus 

 exposing the shell. Cut along the edges of attachment of the 

 mantle and remove the flaps entirely.] 



