72 Zoological Society : — 



they are formed of carbonate of lime, whilst those of the Sponges 

 are of silica. 



In Diadema they take a somewhat triradiate form. 



In Comatula also there are detached spicula in the internal mem- 

 brane of the perisome, which, when mounted in Canada balsam, form 

 beautiful polarizing objects. 



The higher forms of Echinoderms, such as the Holothuriadce, have 

 their skeleton formed entirely of scattered spicula, except the oral 

 ring ; in each species the spicula are of a peculiar form : and all 

 microscopists know the wonderful anchor-shaped spicula and plates 

 in Synapta, and the curious wheels of Myriotrochus and Chirodota. 



Feb. 26, 1861.— John Gould, Esq., V.P., in the Chair. 



On some Points relating to the Habits and Anatomy 

 of the Oceanic and of the Freshwater Ducks, and 

 also of the Hare (Lepus timidus) and of the Rabbit 

 (l. cuniculus), in relation to the question of hy- 

 BRIDISM. By Edwards Crisp, M.D., F.Z.S., etc 



This communication was suggested by the exhibition at our last 

 meeting, by Mr. Bartlett, of four hybrid ducks between the Summer 

 Duck (A. sponsa) of North America, the Pochard (Fuligula ferina), 

 and the Ferruginous Duck (Fuligula nyroca). Mr. Bartlett thought 

 that the progeny of these hybrids would be prolific. In the discussion 

 which followed concerning these birds, I expressed my belief that 

 the hybrid between the hare and the rabbit was a much more re- 

 markable occurrence, taking the habits and the anatomy of the ani- 

 mals into account, than that of a cross between an oceanic and a 

 freshwater duck. From this opinion several of the members dissented. 



It will now be my object to make a fair investigation of this 

 matter ; and as the question of hybridism is one becoming daily of 

 greater importance, I think that our time will not be unprofitably 

 occupied, more especially as the comparisons I am about to institute 

 wid, I think, furnish some matters of physiological interest. 



And first, of the Ducks ; and 1 speak chiefly of British ducks. In 

 this family of birds there is, for the most part, a great general resem- 

 blance, whether we look to their habits or to their anatomy. They 

 have been divided into the Oceanic and Freshwater ducks; but it must 

 be observed that they both frequent the sea, and also the freshwater 

 rivers, although the first-named ducks are more limited to the ocean, 

 to which their structural peculiarities render them better adapted. 

 Their flesh, as regards flavour, has the same character, although 

 modified somewhat by the nature of the food. In the sexual * dif- 

 ferences of colour (excepting the genus Tadorna) there is a great 

 general resemblance ; and the same may be said, as far as we know, 

 of the period of incubation. The eggs, comparatively speaking, 

 both as regards number and appearance, are very uniform. Their ni- 

 dification, too, including the abstraction of down from the body of 



* I do not speak of the changes of plumage in the oceanic ducks, hecause we 

 have yet much to learn respecting this matter. 



