24 NUDIBRANCHIATA. 



few other genera as a distinct group, under the name 

 of ' Phlebenteres," proposed by Prof. Quatrefages, was 

 based on similar grounds, and gave rise to a noted and 

 warm discussion. When kept in confinement, Nudi- 

 branchs enjoy a considerable tenacity of life, although 

 any impurity of the water or an extreme change of 

 temperature affects them very sensibly. This should 

 be borne in mind by all amateur naturalists who wish 

 to preserve these pretty creatures in an aquarium. 

 The littoral species can support a greater variation of 

 temperature than those from deep water; indeed the 

 former will live for a considerable time out of water in 

 a moist saline atmosphere. Their power of enduring 

 abstinence is remarkable. " We have kept them for 

 weeks, and even months, without food, and have ob- 

 served but little diminution of their vital energy." 

 They are, however, very voracious, and are animal- 

 eaters; their food consists of other mollusks, sea-ane- 

 mones, zoophytes, and sponges, the Eolides sometimes 

 devouring weaker individuals of their own kind. Nearly 

 all possess an odontophore or " tongue " armed with 

 recurved spines. In some species the whole of the lin- 

 gual processes do not amount to 112 ; in Tritonia Hom- 

 bergi there are upwards of 36,000. Tethys has neither 

 jaws nor a tongue. This apparatus is rather a prehen- 

 sile than rasping instrument. " In Eolis the protruded 

 jaws lay hold of its prey, cutting out lump after lump, 

 which the tongue, advancing, seizes by the aid of its 

 recurved spines, and with a backward motion carries to 

 the entrance of the oesophagus." It is supposed that 

 most of them are very short-lived, which may account 

 for the periodical appearance of certain species within 

 tide-marks in particular places, and for their usually 

 disappearing soon after the breeding-season. Mr. 



