1062 MR. CYUTL CROSSLAXD OX 



49. Warnino- Coloration in a Nndibrancli Mollusc and iu 

 a Chameleon. By Cykil Ckossland, F.Z.S. 



[Received June 12, 1911 : Eead June 27, 1911.] 



I. Warning Coloration in Chromodorjs. 



Since the discov^ery of Avarning coloration thei-e has been a 

 tendency to attribnte protective value to displays of biilliant tints 

 which further observation has rendered doubtful, and the instances 

 in which actual protection luis been experimentally proved are not 

 so numerous but that one more has some value. 



The Chromodorids are, as their name implies, a family of Nudi- 

 brancbs characterised l)y the development of colour shown by all 

 its members. Having collected a large number during the past 

 ten years, I may say that none of the fami]_y has been wanting in 

 this characteristic, except perhaps Casella atromarginata, which, 

 though handsomely, is not brilliantly, tinted. In this 1 merely 

 corroborate the general expei'ience of marine collectors. Besides 

 this universality of colour the family is well defined structui'ally ; 

 indeed for the class the structure is remarkably uniform. The 

 usual depressed form of body, more or less ample mai-gin, broad 

 foot, and feathery, usually tripinnate gills, are, in the more typical 

 Chromodorids, replaced by the opposite characters. A narrow foot 

 iniderlies a high body, tlie mantle is a mere shelf a,long the top 

 of its vertical sides, and the gills are simply pinnate *. Internally 

 tlie stomach is entirely embedded in the liver. 



There is a smaller section of the family in which these char- 

 acters are less marked, the body having a wider mantle ; in some 

 s )ecies a few of tlie gills are branched and the stomach is partly 

 free from the liver, thus indicating a connection with the ordinary 

 forms. 



Otherwise structure is so uniform throughout the group, that 

 without detailed description of the colours of the living animal 

 identification of the species is impossible. Even with this descrip- 

 tion in full, determination of species is difficult," variation being- 

 very considerable so that, e. g,, what one observer sees as black 

 bands on a white ground is to another white lines on a black 

 body t. 



* Are these simply-pinnate <?ills the pviniitive fonu of Nudilii-andi jrill, a moditi- 

 cation of the prosobranch ctenidium ? The highly specialised Chromodorids sn])ply 

 the answer, since it is the less specialised members of the family that have the more 

 complex gills. A detailed study of the Chromodorid gill would show that its stru<'- 

 ture is more complex than the term " simply i)innate " leads one to sujipose, and 

 jjossibly woiild show details of higher organisation than do the ti'iiiinnate feathery 

 gills of ordinary Dorids. In the development of these gills from an originally irregular 

 vascular Hap of skin, the tripinnate arrangement wouhl be the earlier stage to he 

 reached. 



f Chromodoi-ls qundricolnr Eliot, .Touru. Linn. Soc, Zool. xxxi. Nov. 1908, p. 107 

 ■=C. eUzahethmn, P. Z. S. 1901, p. 392, PI. xxiv. tig. 4. Some other Chromo- 

 dorids are here figured including C.nigrostriato, a variety of the C. dianlii 

 referred to later in this ])aper anil a goad example of the variation now 

 discussed. 



