708 ' REPORT— 1895 



of losing his intellectual life in the weary maze of microtome methods and tran- 

 scendental cytology. The old Greek myth of the Libyan giant, Antreus, who 

 wrestled with Hercules and regained his strength each time he touched his mother 

 earth, is true at least of the zoologist. I am sure he derives fresh vigour from 

 every direct contact with living nature. 



In our tanks and artificial pools we can reproduce the Littoral and the Lami- 

 narian zones ; we can see the methods of feeding and breeding — the two most 

 powerful factors in influencing an animal. We can study mimicry, and test 

 theories of protective aud warning colouration. 



The explanations given by these theories of the varied forms and colours of 

 animals were first applied by such leaders in our science as Bates, Wallace, and 

 Darwin, chiefly to insects and birds, but have lately been extended, by the investi- 

 gations of Giard, Garstaug, Clubb, and others, to the case of marine animals. I 

 may mention very briefly one or two examples. Amongst the Nudibranchiate 

 Mollusca — familiar animals around most parts of our British coasts — we meet 

 with various forms which are edible, and, so far as we know, unprotected by any 

 defensive or oflenslve apparatus. Such forms are usually shaped or coloured so as 

 to resemble more or less their surroundings, and so become inconspicuous in their 

 natural haunts. Dendronotus arborescens, one of the largest and most handsome 

 of our British Nudibranchs, is such a case. The large, branched processes on its 

 back, and its rich purple-brown and yellow markings, tone in no well with the 

 masses of brown and yellow zoophytes and purplish-red seaweeds, amongst which 

 we usually find Dendronotus, that it becomes very completely protected from 

 observation ; and, aa I know from my own experience, the practised eye of the 

 naturalist may fail to detect it lying before him in the tangled forests of a shore- 

 pool. 



Other Nudibranchs, however, belonging to the genus Hulis, for example, are 

 coloured in such a brilliant and seemingly crude manner, that they do not tone in 

 with any natural surroundings, and so are always conspicuous. They are active in 

 their habits, and seem rather to court observation than to shun it. When we 

 remember that such species of Uolis are protected by the numerous stinging cells 

 in the cnidophorous sacs placed on the tips of all the dorsal processes, and that 

 they do not seem to be eaten by other animals, we have at once an explanation of 

 their fearless habits and of their conspicuous appearance. The brilliant colours are 

 in this case of a warning nature for the purpose of rendering the animal provided 

 with the stinging cells noticeable and recognisable. But it must be remembered 

 that in a museum jar, or in a laboratory dish, or as an illustration in a book or on 

 the wall, Dendronotus is quite as conspicuous and striking an animal as Eolis. In 

 o'-der to interpret correctly the effect of their forms and colours, we must see them 

 alive and at home, and we must experiment upon their edibility or otherwise in the 

 tanks of our biological stations.^ 



Let me give you one more example of a somewhat different kind. The soft, 

 unprotected mollusc, Lmnellaria perspicua, is not uncommonly found associated (as 

 Giard first pointed out) with colonies of the compound Ascidian Leptodinum 

 maculatum, and in these cases the Lamellaria is found to be eating the Leptodinum, 

 and lies in a slight cavity which it has excavated in the Ascidian colony, so as to 

 be about flush with the general surface. The integument of the mollusc is, 

 both in general tint and also in surface markings, very like the Ascidian 

 colony with its scattered ascidiozooids. This is clearly a good case of pro- 

 tective colouring. Presumably the Lamellaria escapes the observation of its 

 enemies through being mistaken for a part of the Leptodinum colony ; and the 

 Leptodinum, being crowded like a sponge with minute sharp-pointed spicules, is, I 

 suppose, avoided as inedible by carnivorous animals, which might devour such 

 things as the soft unpi-otected mollusc. But the presence of the spicules evidently 

 does not protect the Leptodiimm from Lamellaria, so that we have, if the above 

 interpretation is correct, the curious result that the Lamellaria profits by a protec- 

 tive characteristic of the Le]}todi/iu7n, for which it has itself no respect, or, to put 



' See my experiments on lishes with Nudibranchs in Trans. BioL Sue, Jjixevpool, 

 vol. iv. p. 150 ; and Xature for June 2G, 1890. 



