24 NUDIBRANCHIATA. 



few Other genera as a distinct group, under tlie name 

 of '• Phlebenteres/'' proposed by Prof. Quatrefages, was 

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

 warm discussion. TVTien kept in confinement. Xudi- 

 brancbs enjoy a considerable tenacity of lite, although 

 any impurity of the water or an extreme change of 

 temperature afi*ects 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 Hve 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 httle diminution of their vital energy.''^ 

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

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

 mones, zoophytes, and sponges, the Eolides sometimes 

 devouring weaker indi\iduals of their own kind. Nearly 

 all possess an odontophore or " tongue " armed with 

 recur>-ed spines. In some species the whole of the lin- 

 gnal processes do not amount to 112 ; in Tritonia Horn- 

 bergi there are upwards of 36,rX>0. Ttthys 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-hved, which may account 

 for the periodical appearance of certain species within 

 tide-marks in particular places, and for their usually 

 disappeariag soon after the breeding-season. Mr. 



