52 DESCRIPTION OP NEW 



the young and perfect shells, lying as closely as possible, came from 

 the orifices at the inferior part of the lobe. This I considered con- 

 clusive as regards this species, but I have not been able to decide so 

 satisfactorily as to the mode of the Uniones discharging their young. 

 I have been in the habit of keeping many living specimens in water, 

 that I might observe them at convenience, and have placed them so 

 near the surface of the water, in basins, as to examine their oviducts 

 with a good lens. In one case, only, have I seen any discharge, and 

 this was in a good sized complanatus, which sent out, while I watched 

 it, perhaps a dozen sacciform oviducts in quite a quick succession. My 

 draughtsman, Mr Drayton, happened to be in my room at the time, 

 and witnessed this operation. Frequently, since that period, I have 

 endeavoured to obtain the same result, but in no case has it recurred. 

 I have, therefore, had my doubts (although I then considered it con- 

 clusive) whether it might not have been the effect of accident arising 

 from the unnatural position of the animal — perhaps weakness or ap- 

 proaching dissolution. The ^n. undulata (see Plate XV. fig. 47) seemed 

 nearly ready to spawn. The following observations were made on 

 one which was kept, and opened December 21. The mass of the lobes 

 in this species differs from the Jluviatilis, in presenting a darker ap- 

 pearance and a very curious arrangement of the oviducts. The ova 

 are placed in a kind of sack which lie across the lobe, presenting one 

 end to the stomach and the other to the mantle of the animal. They 

 lie so close together, as to take the form, on the exterior, like the cells 

 of the honeycomb. This is, of course, caused by pressure. Some of 

 these sacks, when carefully removed, were found to contain as many 

 as twelve ova, each with a perfect living shell in it, having a brownish 

 epidermis. 



Fig. a, represents a sack with its ova. 



Fig. 6, represents the ovum with its perfect young shell included. 



Fig. c, represents the honeycomb appearance, and is eight times 

 magnified. 



Among the species which I had under examination, were numerous 

 specimens of U. radiatus, and, very much to my surprise, I found the 

 females putting on two quite different forms as regards the inferior 

 posterior portion of the mantle. 



