Marine Aquarium. 



6235 



I believe, always coloured red. They are abundant on the 'grassy 

 weed on the stones in sandy places in spring. 



Gosse says that Rissooe (including this species) are precarious, but 

 I have not found them so. They eat Conferva3 and weed, like peri- 

 winkles in confinement, but they are often found in abundance on 

 sand-banks where there is no weed at all. They creep with ease 

 over sand, rock and glass : most shell-fish that inhabit sand adhere 

 very imperfectly to stone and glass, but this is not the case with this 

 species. 



Littorina. The common periwinkle is often recommended as a 

 scavenger in the same mode as the fresh-water snails. The very 

 insufficient cleaning they bestow on the sides is generally far more 

 than compensated by the amount of weed they destroy. Though so 

 often kept, this periwinkle does not seem to breed in confinement, 

 and its spawn is little known. The viviparous species breed freely : 

 L. saxatilis, one of the varieties of L. rudis, began to breed in 

 January. The young have chestnut-brown shells and w^hite animals : 

 the signs of immaturity are the uniform thickness of the tentacles and 

 their bluntness, the large size of the head in proportion to the foot, 

 and the distinctness of the eyes. These little periwinkles do very 

 well in the aquarium, as they are prettily marked and hardy. They 

 require to be closely covered, as they often creep out of the water, 

 and attach themselves by a sticky exudation. |They are here found 

 in the highest part of the littoral zone, or rather high up on a light- 

 house in the lower part of the littoral zone. 



Nudibranchs are noted for what is called their delicacy of consti- 

 tution. The real difficulty in keeping them is to supply them with 

 appropriate food. A Doris will dwindle away to half its original 

 size before it will give up the ghost : they die from starvation. Doris 

 pilosa is hardier than D. bilamellata, and some of the small species 

 seem to live still better. I never kept one more than tvvo months, 

 but I never paid them proper attention. They feed on Bryozoa 

 and small zoophytes, and spawn in spring and autumn. The spawn 

 ofD. pilosa is developed in a few days. The free-swimming larva3 

 all die away before casting their shells ; they cluster about the sur- 

 face of the water in considerable numbers. They are often compared 

 to Pteropoda, but their lobes or wings are not moveable, and their 

 easy gliding motion is caused by ciliary and not muscular action. 

 Though so very minute, their peculiar motion enables them to be 

 distinguished by the naked eye. The free-swimming larvae of 

 barnacles can be distinguished in the same manner. 



