BRITISH NUDIBRANCHIATE MOLLUSCA. 23 



removed the animal will crawl about in perfect unconcern ; and in this state they have been 

 observed to copulate. The power of renewing lost or injured parts is enjoyed by these little 

 Mollusks in common with the rest of the class, and it is interesting to observe the progress of 

 their growth, which may readily be done when the animals are kept in a glass vessel. In an 

 Eolis so confined, and in a great measure deprived of food, we have seen the papillae reappear 

 and attain a considerable size in three or four days. At first they resemble tubercles, without 

 central gland, which, however, soon makes its appearance, and assumes its normal character. 



Their tenacity of life when kept in confinement varies much in the different species, but 

 is greater than in many other marine animals. Any impurity in the water, or too great change 

 of temperature, affects them very sensibly, so that it is difficult to keep them alive in warm 

 weather, particularly those from deep water. The littoral species can sustain a greater change 

 of temperature, and may be kept alive for a considerable time out of water in a moist saline 

 atmosphere, but they die almost immediately when deprived of moisture. Their power of 

 enduring abstinence is remarkable. We have kept them for weeks, and even months, without 

 food, and have observed little diminution of their vital energy. In such cases they generally 

 lose a good deal of colour and become very transparent. 



But, though so patient and long-suffering in the endurance of hunger, these little animals 

 are very voracious. The greater number of them are carnivorous ; living principally upon 

 zoophytes and sponges. The Alcyonium digitatum is a favorite food with the Tritonia ; and 

 the Actinia and Lucenarice often fall a prey to the attacks of the Bolides. These latter, indeed, 

 do not scruple occasionally to devour the weaker among their own brethren, as we have 

 elsewhere recorded. Sir J. G. Dalyell states that his Eolis histrix {Brummondi) "fed voraciously 

 on mussel, and on the common periwinkle, whereof large portions were swallowed entire ;" 

 and he thinks that Goniodoris nodosa feeds upon Ascidia papilla {Cynthia rustica), to which he 

 attributes the reddish colour observed in the viscera. This colour, however, is caused by the 

 liver and ovary. We have taken from the stomach of Eolis papillosa minute specimens of the 

 common mussel, and a small Terebra from that of Tethys. The more common food of the 

 tribe, however, is the flexible zoophytes. Until lately the Dorides have been considered 

 vegetable feeders, but this would appear not to be the case. Doris tuber culata feeds upon the 

 common encrusting sponge {Halicltondria panicea), and sponges and zoophytes seem to 

 constitute the food of most of the others. A few of the gregarious Nudibranchs, such as 

 Polycera quadrilineata, Hermcea dendritica, and Alderia modesta, which congregate on marine 

 algse, appear to be phytivorous ; but Eolis despecta, and E. exigua, though not unfrequently 

 gregarious on the fronds of Laminaria digitate^ are only found on those parts of the plants that 

 are covered with the parasitic zoophytes, Laomedea geniculaia and L. gelatinosa, on which they 

 feed and deposit their spawn. 



Most of the species that are found between tide-marks make their appearance periodically, 

 and the common kinds are generally found in considerable numbers for a time, extending from 

 one to three months, after which they almost entirely disappear. This is their breeding 

 season, and it is generally considered that these animals live mostly beyond low-water mark 

 for a great part of the year and come into shallower water to spawn, as is the case with several 

 tribes of marine animals. This opinion, however, does not accord with what is known of the 

 habits of other Mollusks. It is not likelv that creatures so defenceless and limited in locomotive 



