508 Artliur E. Shipley 



attached at Ijoth euds to the body wall ßg. 4 ov] , but a little below the 

 origiu of tbe adjustor muscles aud the entrance of tbe li ver luto the 

 stomaeh; this membrane becomes broader, its inner end becomes attached 

 to the lateral walls of the stomach. its outer to the line of attachment of the 

 lophophore aud thus it forms the gastro-parietal band. This as was meu- 

 tioned above divides the body cavity into two halves, in the ventral half 

 the liver lies, in the other the ovaries and the greater part of the muscles. 

 The two halves communicate below. The ovaries of the ventral shell 

 lie, one in each half of the body cavity, which is bere divided into two 

 lateral portions by the presence of the median ridge spoken of in the 

 description of the shell. These parts of the body cavity communicate 

 with each other and with the remainder, at the posterior extremity. 



Each ovary appears to be formed of a membrane continuous with 

 the body wall: this bears on each side a number of ova which vary 

 greatly in size. The membrane is covered with epithelium continuous 

 with that of the body cavity, except where the ovaoccur and these seem 

 to be as Van Bemmelen suggests modified epithelium cells. Each ovum 

 is surrounded by a very delicate capsule in which nuclei occur. At the 

 most anterior end the ova are very small, but gradually become larger 

 as they approach the posterior ; they are usually more or less round 

 unless they exist in great numbers when they become angular by mutuai 

 pressure. They are very granular and stain well except the nucleus 

 which only stains faintly or not at ali, tbe nucleolus again staining deeply. 

 Both these structures are very large , the nucleolus being sometimes of 

 such a size that the nucleus assumes the shape of a new moon. 



When the eggs are ripe they drop off into the body cavity, the 

 capsule apparently bursting. In the body cavity they are taken up by 

 the inner end of the oviduct aud thus pass into the brood pouch. 



The o\dducts open internally by a funnel shaped mouth which looks 

 towards the dorsal shell (fìg. S od). The outer lip of the mouth is con- 

 tinuous with that part of the body wall which forms the inner boundary 

 of the brood pouch, the inner lip is beut towards the middle line and is 

 continuous with a connective tissue band which passes to support the 

 posterior end of the intestine. This represents the ileo-parietal band of 

 Huxley; it is very slight. The oviduct then runs round the ventral 

 wall of the brood pouch and opens into this pouch by a small mouth 

 dose under the posterior border of the lophophore. 



The walls of the oviducts consist of a connective tissue basement, 

 lined by glandulär cells which contain browu concretious ; hence it is 

 very probable that they act as secretory organs in addition to their 



