September 19, 1895] 



NATURE 



499 



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 offensive 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. Den- 

 droiiotiis aihorescens, one of the largest and most handsome of 

 our British Nudibranchs, is such a case. The large, branched 

 ]jrocesses on its back, and its rich purple-brown and yellow 

 markings, tone in so well with the masses of brown and yellow 

 zoophytes and purplish-red seaweeds, amongst which we usually 

 find Deiidronotus, that it becomes very completely protected 

 from observation ; and, as 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 Eolis 

 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 Eolis 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 laborator)' dish, or as an illastralion in 

 a book or on the wall, Deiidrmiotus is quite as conspicuous and 

 striking an animal as Eolis. In order 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 exam])le of a somewhat different 

 kind. The soft, unprotected mollusc, Lamellaria perspictia^ 

 is not uncommonly found associated (as Giird first pointed out) 

 with colonies of the compound Ascidian I^ptoclintiin macitlatiim, 

 and in these cases the Lamellaria is found to be eating the 

 LeptoiltHitm, 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 

 ilsscattere<l 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 Leptciliiiuiii colony ; and the Leploclinum, 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 unprotected mollu.sc. But the presence 

 of the spicules evidently does not protect the Leptoclinum from 

 Lamellaria, so that we have, if the above interpretation is 

 correct, the curious result that the Lamellaria profits by a pro- 

 tective characteristic of the Zcy>to/jK«/«, for which it has itself 

 no respect, or, to put it another way, the Leploclinum is pro- 

 tected against enemies to some extent for the benefit of the 

 L.amellaria, which preys upon its vitals. 



It is, to my mind, no sufficient objection to theories of pro- 

 tective and warning colouration that careful investigation may 

 from time to time reveal cases where a disguise is penetrated, a 

 jjrolection frustrated, an offensive device supposed to confer 

 inedibility ajiparently ignored. We nuist bear in mind that the 

 enemies, as well as their l)rey, are exposed to comi^etition, are 

 subject to natural selection, are undergoing evolution ; that the 

 pursuers and the pursued, the eaters and the eaten, have been 

 evolved together ; and that it may be of great advantage to be 

 protected from some, even if not from all enemies. Just as on 

 land, some animals can browse upon thistles whose "nemo me 

 impune lacessit" spines are supposed lo confer immunity from 

 attack, so it is quite in accord with our ide.is of evolution by 

 means of natural selection to suppose that some marine animals 

 have evolved an indifference to the noxious sponge or to the 

 bristling Ascidian, which are able, by their defensive character- 

 istics, like the thistle, to repel the majority of invaders. 



Although we can keep and study the Littoral and Laminauan 

 animals at ease in our zoological stations, it may jierhaps be 

 (|uestioned how far we can reproduce in our exjierimental and 

 observational tanks the conditions of the "CoraUine" and 

 (he " Deep-mud " zones. One might suppose that the pressure 



} See my experiments on Fishes with Nudibranchs, in Trans. Biol. Soc, 

 C.iverpool, vol. iv. p. 150 ; and Nature for June 26, 1890. 



NO. I 35 I, VOL. 52] 



— which we have no means as yet for supplying' — and which at 



30 fathoms amounts to nearly 100 lbs. on the square inch, and 

 at 80 fathoms to about 240 lbs., or over 2 cwt. on the square 

 inch, would be an essential factor in the life conditions of the 

 inhabitants of such depths, ajid yet we have kept half a dozen 

 specimens of Caloearis macandrees, dredged from 70 to 80 

 fathoms, alive at the Port Erin Biological Station for several 

 weeks ; we have had both the red and the yellow forms of 

 Sareodiclyon catenala, dredged from 30 to 40 fathoms, in a 

 healthy condition with the polypes freely expanded for an in- 

 definite ])eriod ; and Mr. Arnold Watson has kept the Polj-noid 

 worm, Panthalis oerstedi, from the deep mud at over 50 fathoms, 

 alive, healthy, and building its tube under observation, first for 

 a week at the Port Erin Station, and then for many months at 

 Sheffield in a comparatively small tank with no depth of water. 

 Consequently it seems clear that, with ordinary care, almost any 

 marine animals from such depths as are found within the British 

 area ir.ay lie kept under obser%ation and submitted to experiment 

 in healthy and fairly natural conditions. The Biological Station, 

 with its tanks, is in fact an arrangement whereby we bring a 

 portion of the sea with its rocks and bottom de|»sits and sea- 

 weeds, with its inhabitants and their associates, their food and 

 their enemies, and place it for continuous study on our laboratory 

 table. It enabUs us to carr>' on the bionomical investigations 

 to which we look for information as to the methods and progress 

 of evolution ; in it lie centred our hopes of a comparative 

 physiology of the invertebrates — a physiolog)' not wholly medical 

 — and finally to the Biological Station we confidently look for 

 help in connection with our coast fisheries. This brings me to 

 the last subject which I shall touch upon, a subject closely related 

 both to Oceanography and Bionomics, and one which depends 

 much for its future advance upon our Biological Stations — that is 

 the subject of 



Aquiculture, 



or industrial Ichthyology, the scientific treatment of fishery in- 

 vestigations, a subject to which Prof. M'Intosh has first in this 

 country directed the attention of zoologists, and in which he has 

 been guiding us for the last decade by his admirable researches. 

 What chemistry is to the aniline, the alkali, and some other 

 manufactures, marine zoologj- is to our fishing industries. 



Although zoology has never appealed to popular estimation as 

 a directly useful .science having industrial applications in the 

 same way that Chemistry and Physics have done, and con- 

 sequently has never had its claims as a subject of technical 

 education sufficiently recognised ; still, as we in this Section are 

 well asvare, our subject has many technical applications to the 

 arts and industries. Biological principles dominate medicine 

 and surgery. Bacteriology, brewing, and many allied subjects 

 are based upon the study of microscopic organisms. Economic 

 entomology is making its value felt in agriculture. Along all 

 these and other lines there is a great future opening up before 

 biology, a future of extended usefulness, oi popular appreciation, 

 and of value to the nation — and not the least important of these 

 technical applications will, I am convinced, be that of zoolog)' 

 to our fishing industries. When we consider their enoniious 

 annual value — about eight millions sterling at first hand to the 

 fisherman, and a great deal more than that by the time the pro- 

 ducts reach the British public, when we remember the very large 

 proportion of our population who make their living directly or 

 indirectly (as boatbuilders, net-makers, i.\:c. ) from the fisheries, 

 and the still larger proportion who dejiend for an important 

 element in their food supijly upon these industries ; when we 

 think of what we pay other countries — Erance, Holland, Norway 

 — for oysters, mussels, lobsters, <S:c., which we could rear in this 

 country if our sea-shores and our sea-bottom were properly 

 cultivated ; and when we remember that fisherj- cultivation or 

 aquiculture is applied zoology, we can readily realise the enor- 

 mous value to the nation which this direct application of our 

 science will one day have — perhaps I ought rather to say, we 

 can scarcely realise the extent to which zoology may be made 

 the guiding science of a great national industrj'. The flourish- 

 ing shellfish industries of France, the oyster culture at Arcachon 

 and Marennes, and the mussel culture by bouchots in the Bay 

 of Aiguillon, show what can be done as the result of encourage- 

 ment and wise assistance from Government, with constant 



t Following up M. Regnard's experiments, some mechanical .arrangement 

 whereby w.-Uer could t>e kept circulating .ind aerated under pressure in closed 

 tanks might be deWsed, and ought to be tried at some zoological station. I 

 learn from the Director at the Plymouth Station that some of the. anim.tls 

 from deep water, such as Polyzoa, do not expand in their tanks. 



