Ill TROTECTIVE COLORATION 73 



when the experiments were conducted under conditions which 

 made the scene as much like ' real life ' as possible, did not 

 agree with Professor Herdman. The Ancula crawled over 

 various parts of the tank for several days untouched by the 

 fish, who sometimes went close to them and looked at them, 

 but never attempted to taste them. Experiments with species 

 whose colours were protective, such as Dcndronotus, were also 

 conducted, and the decided edibility of these species was 

 established, the fish competing eagerly for them, and tearing 

 them rapidly to pieces. 



Mr. W. Garstang, of the Plymoutli Laboratory of the Marine 

 Biological Association, confirms ^ Professor Herdman's views as 

 to the shape and colour of Opisthobranchs. Pleurohranclius 

 memlranaccus is known to secrete, on the surface of the body, 

 an acid which reddens blue litmus paper. It is, therefore, no 

 doubt distasteful to fish, which all abominate the taste of acids, 

 and is conspicuously marked with red -brown and yellowish 

 ' warning ' colours. Saminea and Philine, on the other hand, 

 are good to eat, and consequently possess ' protective ' colora- 

 tion. EuTicina Hancocki, which is of a brown colour, crawls 

 over brown mud and weeds, but avoids green weeds, on 

 whose surface it would appear conspicuous. Elysia viridis 

 varies its colour according to its habitat, being green when 

 on green weeds, and dark olive, brown, or reddish brown, on 

 pools among tufts of littoral algae. Green specimens of 

 Hermaea dendritica were kept in captivity, and placed in a dish 

 with green and red sea -weeds. They were never observed 

 crawling upon the red weed, upon which they would have 

 been very conspicuous. Archidoris flammea occurred on bright 

 red sponges, to wliich its colour was so closely assimilated 

 that Mr. Garstang at first quite overlooked it. Goniodoris 

 castanea was found under stones, feeding on compound Ascidians 

 {Botryllus), which it sufficiently resembled to be very in- 

 conspicuous in that position. 



iVgain, Jorunna Johnstoni lives - upon stones on our southern 

 coast, associated with a certain sponge (Halichondria sp.), wliich 

 it resembles so closely in outline, in colour, in character of 

 surface, and in its projecting plumes, as to make it very 



' Journ. Mar. Biol. Ass. N. S. i. p. 418 f. 

 ^ Garstang, Conchologist, ii. p. 49. 



