EGGS OF MOLLUSC A. 237 



culinary object. The egg- cases of the whelk are very 

 common objects by the seaside, of a light brown 

 colour, resembling a large head of hops. Each capsule 

 contains an individual embryonic shell, perfectly 

 formed, and not exceeding a pin's head in size. When 

 they are present in a storm-tossed specimen of egg- 

 cases, they are detached, and rattle inside the cap- 

 sules when shaken. Haliotis tuberculata or "Venus' 

 ear," is another marine mollusc of much service in 

 the aquarium as a vegetable scavenger. It is lively 

 and attractive both on account of the graceful shape 

 of the animal, and the parasitic weeds which adorn 

 the shell. Nassa purpara (or dog-whelks), top 

 shells (Trochi), murex, Pileopsis, Cyprea, Aporrhais 

 pespelicani (or pelican's foot shell), Natica monilifera 

 a common and prettily marked univalve shell, 

 easily domesticated Turitella, Bulla, &c., are other 

 univalves which are kept with more or less ease in the 

 Brighton, Crystal Palace, and Manchester Aquaria. 



The group of shell-less molluscs answering in the 

 sea to the slugs upon land have been favourites in 

 the marine aquarium ever since Alder and Hancock, 

 and especially Gosse, wrote so attractively about 

 them twenty-five years ago. But the sea-slugs breathe 

 by means of gills, which are usually borne on the 

 back, uncovered by any shell, hence the name given 

 to the group of Nudibranchiata, or " naked-gilled." 

 These branchiae or gills are usually coloured, or 

 prismatically tinted, so as to render their possessors 



