562 H. p. KJERSCHOW AGERSBORG 



These coelomic cavities then fuse and later by a process of 

 special growth form a peritoneal funnel that opens to the outside 

 on either side. The gonad develops from the wall of the coelom ; 

 then, together with the rudimentary left peritoneal funnel, it 

 becomes constricted off from the main division of the coelom 

 (the pericardium), forming a small genital sac. From the wall of 

 this sac, the genital duct grows out, and joins an epidermal 

 invagination like the peritoneal funnel of the right side. 



In M. leonina the perigonadium is situated caudoventrally 

 in the perivisceral cavity. It has a complex duct-system which 

 opens on the right side near the anterior end of the trunk of 

 the body (PL 27, figs. 2, 3, P ; PL 37, fig. 81). The single 

 kidney (nephrocoel) is situated dorsally and communicates 

 internally Avith the pericardium through the renal syrinx and 

 e^xternally through the ureter Avhicli opens on the left side of, 

 and close to, the anal pore. The perigonadial coelom (peri- 

 gonadium) and pericardium are completely separated by 

 the visceral cavity or vascular (haemocoels) cavities. These 

 cavities are blood-spaces into which the blood percolates from 

 the arterial vessels, bathing the visceral organs. In Chitons, 

 * A separation has taken place in the genital region of the 

 coelom from the renal ; the gonad then acquires special ducts 

 which may not be homologous with the peritoneal funnels ' 

 (Goodrich, 1895 : p. 486). 



(1) The Hermaphrodite Gland. 



It is a well-known fact that the gonads among nudibranchs 

 and many other molluscs are hermaphroditic, but the duct 

 system of the two different functional regions varies relative 

 to their complete development. Some authors who have 

 worked on the Elysiadiidae (Allmann, Hancock, Souleyet, 

 Gegenbaur, &c.) maintained that the male and female parts 

 of the hermaphrodite gland are separate as are the ducts 

 (vide Pelseneer, 1891). It has been shown by Pelseneer (1891), 

 who worked on several genera of the group in question, that 

 the same part of the gland is both male and female ; some of 

 the follicles of the hermaphrodite gland among certain 



