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THE BOOK OF NATURE STUDY 



as noted above, their spawn is interesting, are rather disconcert- 

 ing in captivity because of their tendency to crawl out of the 

 water and get lost, but the tops or trochi, with conical shells, 

 often prettily marked, are more satisfactory. They are vege- 

 tarian forms like the periwinkles, but the animal, which has 

 long tactile processes or cirri, is more attractive in appearance. 

 As to the bewildering complexity of sea slugs or Nudibranchs, 

 we cannot do much more than urge the teacher if possible to 

 consult the beautiful plates of Alder and Hancock's Monograph 

 of the British Nudibranchiate Mollusca (Ray Society), or make a 



FIG. 68. A common nudibranch (Eolis rufibranchialis). (After Alder and Hancock.) 



pilgrimage to Newcastle-on-Tyne Museum to see the originals, 

 before beginning to hunt the pools for specimens. As these 

 plates will show, there are a great number of British species. Not 

 a few are quite common on the rocks in spring when they lay 

 their eggs, while others are common all the year round, but are 

 apt to be overlooked because of their small size. They are 

 carnivorous, feeding especially on zoophytes, and a capital way 

 of obtaining the more delicate forms is to take at random a hand- 

 ful of sea-firs from a pool, and put them into a dish when some 

 delicately coloured sea-slug may quite possibly reveal itself. 

 The commonest form is perhaps Doris, already mentioned 

 which has a circlet of gill plumes round the dorsal anus, but the 

 species of Eolis with the back covered by numerous slender papillae 

 are also abundant in pools. (See also the coloured plate.) 



