SOME NUDIBRANCHS 107 



off by 10th September. Four days after these young 

 examples were got at Joppa, namely, on 29th July, two full- 

 grown specimens were found on Bryopsis from rock-pools 

 at Longniddry Bay. 



H. dendritica, with its characteristic "dendritical green 

 markings," was described by Alder and Hancock some 

 seventy years ago, from numerous examples found in 

 Torbay, Devon, feeding on the seaweed Codium tomentosum. 

 In this account of the mollusc its length is given as three- 

 tenths of an inch { 7\ mm.), and ova in spawn deposited 

 on 13th May had hatched by the 22nd. The only Scottish 

 records of Codium tomentosum that we can recall are from 

 the west coast and Orkney. Though superficially Codium 

 and Bryopsis look very different, they are in reality quite 

 closely related, since both belong to the Siphoneae, a small 

 non-septate group of the green Algae. Doubtless, therefore, 

 they possess in common some property upon which the 

 Hernuza is dependent. Hermaeids, it appears, do not, strictly 

 speaking, " eat " the substance of their food-plants, but 

 merely scratch the surface and suck the juices thus set free. 1 

 Herein may lie the key to our little nudibranch's predilec- 

 tion, for the Siphoneae, as the name implies, have their 

 vegetative parts composed of long branching tubes with- 

 out dividing walls, and are of a markedly "lubricous" or 

 gelatinous nature. Bryopsis, it should be said, is an annual, 

 growing up in late spring and dying off in autumn. A 

 Herman, with dorsal processes fully extended, browsing, as 

 it were, among the delicate green plumes of Bryopsis, can 

 only be detected with some difficulty, so well does it fit in 

 with its surroundings. 2 



The facts given above would seem to suggest that H. 

 dendritica passes through two generations in the course of 

 a year, one coming to maturity, and spawning, in May and 

 June, the other in July and August. In what stage the 



1 Cf. Suppl. to Alder and Hancock's Monograph, p. 20. 



2 Since this paper was in type we see that H. dendritica has been 

 found on Bryopsis (species not mentioned) at Plymouth, (/ourn. Mar. 

 Biol. Ass., n.s., vol. vii., No. 2, Dec. 190^, p. 277.) 



