The anatomy of Lottia gigantea Gray. 19 



muscular body wall ("neck") is above the duct and a portion of the 

 liver below. In Fig. F (Gn.D) this tube is shown in the same section 

 with the nephridial ends of the reno-pericardial canals, but in reality 

 it would occur a trifle in front of the plane of this section, which is 

 an oblique one. 



In Lottia gigantea the sexes are separate, and there is no pro- 

 gressive change from male to female in the same individual. As soon 

 as there is a definite gonad (when the shell is 10 to 11 mm, longest 

 diameter) there is a sharp differentiation between the males and 

 females. In animals 10 mm in length the ovaries and testes seem to 

 have fully developed products, though the gonad is not relatively so 

 large as in the adult. In fully grown examples, the females much 

 outnumber the males. 



I have found eggs free in the large right kidney sinus at Christ- 

 mas, but unfortunately did not preserve those individuals to examine 

 the state Of the gonoduct. 



Secondary Body Cavity and Pericardium. 



The pericardium is described in connection with the heart. It is 

 & triangular cavity situated on the left side of the body, well in 

 front, so that a portion overlies the head. It communicates with the 

 lumen of the right and left nephridia (called by some investigators 

 the "nephridial coelom") by long tubular diverticula, which pass under 

 the renal epithelium, and open by tiny ciliated canals at the summit 

 •of minute papillae, one near each ureter. The long canals are portions 

 of the pericardial cavity, the ciliated funnels being only that part 

 within the papillae. 



The space surrounding the gonad, scarcely more than a potential 

 cavity in the adult with fully developed sex products, belongs to the 

 coelom or secondary body cavity, and not to the pseudhaemal spaces 

 or primary body cavity. One can argue of course that this cannot 

 be logically settled till the development is thoroughly studied. The 

 space in question, however, is lined with the thin coelomic epi- 

 thelium, is not connected with the blood system in any way, and finally 

 opens by a slender duct (the gonoduct) into the lumen of the right 

 nephridium. The last fact seems to be conclusive evidence that the 

 space does not belong to the pseudhaemal system, to which for in- 

 stance the lacunae among the liver lobules appertain. In very small 

 individuals, before the sex products are formed, one can see a veri- 

 table cavity beneath the intestine and liver. In this, sex cells begin 



2* 



