THE INSTINCT OF SELF-CONCEALMENT AND THE CHOICE OF COLORS IN THE CRUSTACEA.

By ROMUALD MINKIEWICZ.

(Translated by permission from Revue générale des Sciences pures et appliquées, Paris, 20th year, No. 3, February 15, 1909.)

In the following pages I shall give a brief though sufficiently detailed account of the results of my investigations carried on since 1903, which have already afforded material for a long series of publications." This series, beginning with a short article that I published (in Polish) in 1905, in a weekly scientific review at Warsaw (Przyroda Nature), is yet, however, far from being finished.

I. THE SELF-DISGUISING ANIMALS.

Although I am the first seriously to undertake this study, the strange phenomenon of self-concealment has in a general way long been known. I am not considering here animals recently discovered

R. Minkiewicz: (1) Krab-ogrodnik. Rev. polonaise, Przyroda, vol. 2, No. 10, Varsovie (mars 1905).

(2) Sur le chromotropisme et son inversion artificielle. Comptes Rendus Ac. Sc., Paris, t. 143, No. 21 (nov. 1906).

(3) Le rôle des phénomènes chromotropiques dans l'étude des problèmes biologiques et psychophysiologiques. C. R., t. 143, No. 23 (déc. 1906).

(4) Chropotropism and phototropism. (Translation of the two preceding notes.) Journ. of Neurology and Comparative Physiology, vol. 17, No. 1 (1907). (5) Analyse expérimentale de l'instinct de déguisement chez les Brachyures oxyrhynques. Arch. de Zool. expériment. et génér., 1907 (4), vol. 7, No. 2.

(6) Próba analizy instynktu metoda objektywna: porównawczai dóswiadczaina, Revue polonaise de Philosophie, vol. 10, fasc. 3-4, et vol. 11, fasc. 1-2, Varsovie (1907-8).

(7) L'étendue des changements possibles de coleur de l'Hippolyte varians Leach. C. R., t. 147, No. 20 (nov. 1908).

(8) Etude expérimentale du synchromatisme variable de l'Hippolyte varians Leach. Bull. internat. de l'Académie Polonaise de Cracovie (nov. 1908).

(9) Sur le chlorotropisme normal des Pagures. C. R., t. 147 (nov. 1908). (10) L'apparition rythmique et les stades de passage de l'inversion expérimentale du chlorotropisme des Pagures. C. R., t. 147 (déc. 1908).

or unfamiliar; on the contrary, many people, including the bathers on the Breton coast, are acquainted with the creatures that I am going

to discuss, which are commonly called by the name of sea-spiders.

These self-disguising Crustacea, although they belong exclusively to the rather restricted group of Brachyura Oxyrhyncha, are very common, not only along all the European coasts (of the Mediterranean, the English Channel and the

FIG. 1.-Disposition of the dorsal hooks in Maja verrucosa M. Edw. (Only the right side is completely drawn.)

FIG. 2. Second left foot, outer side. (Hyas araneus L.)

Atlantic as far as Spitzbergen and Greenland), but also along the coasts of the Far East and southern Asia (Japan, Celebes, Java, Bengal, India, etc.), in the Pacific along the coasts of Tasmania,

FIG. 3.-Group of hooks on a dorsal tubercle. (Hyas araneus L.)

Australia, and New Zealand, and along the coasts of of South America (Peru, Chile, Cuba, Brazil, etc.). Of this group there are more than 70 species belonging to 38 genera and 4 families."

forcibly during the very interesting dredging that we did in the vicinity of the Balearic Islands on board the Roland, of the Arago Laboratory, during the month of August, 1903, form a quite distinct group, possessing extraordinary morphological adaptations which

FIG. 4.-Vertical section made through a dorsal hook and the adjacent parts of the carapace. Beds of chitin, chitogenous epithelium and conjunction tissue. (Hyas coarctatus Leach.)

are not found elsewhere. A Swedish naturalist, Carl Aurivillius, has made an elaborate study of these adaptations, and it is from his work' that I have taken the few drawings here reproduced (figs. 1-7).

a The list published by C. Aurivillius gives only 66 species, but it is far from complete, not containing, for example, a form so common as Maja squinado Latreille.

C. Aurivillius: Die Maskirung der Oxyrrhynchen Dekapoden durch besondere Anpassungen ihres Körperbaues vermittelt. Eine biologisch-morphologische Studie. Svenska Vet.-Akad. Handl., bd. 23, Stockholm (1889).

Of this entire group I personally know in life 14 species belonging to the genera Stenorynchus, Inachus, Acanthonyx, Maja, Pisa, and Lambrus. But although I have made observations on several different species, I shall speak in this article of only two, both belonging to the genus Maja Lamarck (M. verrucosa Milne-Edwards and M. squinado Latreille), species very closely allied and with identical habits.

II. THE SELF-CONCEALMENT OF THE CRABS.

With reference to Hyas araneus Linnæus, a species of the family Majidæ, the process of concealment has been very accurately described by Carl Aurivillius. It is almost identical with that of the species of Maja, which is described below:

Having found an alga (of any kind, red, brown, or green, depending upon circumstances), the crab seizes it with its long, slender claws, puts it first into its mouth, and, while holding it by one end with its maxillipeds, begins to tear it to pieces with its two claws, one drawing it toward its carapace, the other pushing it away.

and

FIG. 5.-Left claw recurved on the back of the animal scraping the hooks of the last group of the upper left line. (Hyas araneus L.)

When a piece, the size and form of which may vary indefinitely, has once been cut off, the crab pushes it with one of its claws between its maxillipeds and whirls it around several times, acting as if it were its prey-a mussel or a piece of fish.

After having rumpled it, it takes it again with one of its claws (indifferently with the left or the right), then extends the claw

FIG. 6. Right claw curved under the

forward as far as possible, and, after making a rotary motion, bends it around over its back" and proceeds to affix the alba upon a group of dorsal hooks, rostral, branchial, etc., moving the claw slightly back and forth until the

ventral surface of the animal toward alga hooks on. Sometimes it at

the branchial hooks of the left side. (H. araneus L.)

taches it on the outer surface of the ambulatory feet, which are

similarly provided with hooks, by flexing the foot and bending it under the ventral face of the carapace.

I have more than once shown this operation to my fellow-laborers in the laboratories of Villefranche-sur-Mer and of Roscoff.

"This movement is seen only in the crabs under consideration.

The proceedings are the same if the crabs are furnished with sponges, hydroids, or compound ascidians instead of algae. If they do not find living material they content themselves with débris, with pieces of the carapace of dead Crustacea, with shells-in fact, with anything that they may find, paper, rags, threads, etc.

The species which we dredged on board the Roland having come from different bottoms and different depths, varied correspondingly in their method of disguise, especially in regard to color; and it is this very fact which suggested to me the idea of undertaking some

FIG. 7.-The same movement seen from the ventral side. (H. coarctatus Leach.)

investigations in regard to the question

of the relation between the color of the covering and that of the environment.

The material suitable for these experiments I found indicated in this passage by M. Hermann Fol:"

I tried once to take away from it (Maja) all the weeds it might have taken for cuttings, and to give it instead bits of hay and of white paper. It conscientiously stuck on its back these objects, which could only serve to make it still more conspicuous than if it had put nothing there at all.

I decided, therefore, to use colored. paper, and employed a fine paper called papier de soie.

The crabs behaved in regard to this material just as if it had been an Ulva (U. lactura Linnæus).

III. EXPERIMENTS MADE IN AN ENVIRONMENT OF VARIABLE COLOR.

§ 1. THE COVERING FOLLOWING THE ENVIRONMENT.

The best preparation for experiments, of which I have made hundreds, is the following:

In an aquarium constructed entirely of glass, the bottom and the sides to a certain height are covered with colored paper pasted to cardboard, so that too much light may not pass through, as the crabs have a strongly marked negative phototropism; they are photophobes, in the psychological language of Vitus Graber and others; that is to say, they avoid the direct light, as well as fire screens and light places. There are then placed in the aquarium a few thoroughly cleaned crabs, not more than two or three, and some pieces of two kinds of papier de soie-one the same color as the environment and the other any different color, no matter what. The shape,

@H. Fol: L'instinct et l'intelligence. Rev. Scient., 3° série, No. 7 (1886).