804 



ZOOLOGICAL SOCIETY BULLETIN. 



amble slowl}' along in a most awkward fashion. 

 If they are ever in a hurry they never give any 

 indication of it by accelerated movements. They 

 are even too slow to fight except with each other, 

 and they appear to be always good friends 

 among themselves. 



Our Libiiiias attain a size of about eighteen 

 inches across the extended legs, with a body a 

 little larger than one's fist. The eggs, which 

 are carried as in the lobster attached to the 

 swimmerets beneath the abdomen, are not as 

 large as the head of a pin, and adult size is ap- 

 parently not reached for several years and after 

 undergoing numerous moults. In the moulting 

 process the old shell ruptures around the rear 

 margin of the carapace and the soft-shelled oc- 

 cupant backs out of the split thus formed. In a 

 few hours it has absorbed an enormous amount 

 of water and lias swelled until it is much larger 

 than it was before. In this condition it begins 

 the secretion of a new shell, within which it con- 

 tinues to grow until all the spaces have been 

 filled, when it must moult again if it is to grow 

 further. This moulting process at first goes on 

 quite rapidly, occurring every few weeks in the 

 very young, but this gradually slows down to 

 perhaps only once a 3'ear as the adult condition 

 is reached. 



The decorating instinct, which has for its pur- 

 pose the protection of the crab by rendering it 

 inconspicuous in its surroundings, is highly de- 

 veloped in the spider crabs. This instinct 

 gradually wears away in Libinia as it ap- 

 proaches maturity, probably because the animal 

 reaches a size in which the strongly calcified, 

 spiny shell is sufficient protection. Numerous 

 investigators have studied this question in vari- 

 ous sorts of spider crabs, but perhaps the most 

 thorough studies have been those of Dr. R. 

 IMinkiewicz on species of Maja occurring on the 

 coast of France. 



The method of attaching the decorative mate- 

 rial to the small recurved or hooked processes 

 on the carapace and legs is described by Dr. 

 Minkiewicz as follows: "Having found an alga, 

 the crab seizes it with its long slender claws, 

 puts it first into its mouth, and while holding it 

 with its maxillipeds, begins to tear it to pieces 

 with its two claws. When a piece has been cut 

 off, the crab pushes it with one of its claws be- 

 tween its maxillipeds and whirls it around sev- 

 eral times. After having rumpled it, it takes it 

 again with one of its claws, extends the claw 

 forward as far as possible, and, after making a 

 rotary motion bends it around over its back and 

 proceeds to affix the alga upon a group of dorsal 

 hooks, moving the claw slightly back and forth 

 until the alga hooks on." 



Instead of algae various other things may be 

 used. The writer has observed spider crabs 

 with hydroids, bryozoa, sponges, ascidians, etc., 

 and if living organisms are not available they 

 will make use of anything within reach that can 

 be utilized — in the aquarium they will use pieces 

 of paper, cloth, string, etc. These may be at- 

 tached to the limbs as well as upon the cara- 

 pace, until the crab may be entirely obscured 

 beneath the mass. 



Dr. Minkiewicz finds that Maja rigidly se- 

 lects in relation to the environment. "If the 

 walls (of the aquarium in use in the experiment) 

 are white they will be covered with white only ; 

 they will take neither green nor yellow nor 

 black; if the walls are green, they will be 

 clothed only in green." Furthermore, when 

 these crabs are clothed in one color they 

 habitually seek concealment in an environment 

 of the same color. An experiment to prove this 

 was made by preparing an aquarium the two 

 ends of which were of different colors. "The 

 crabs are invariably seen to make their way to- 

 ward the half of the aquarium corresponding in 

 color to tlieir covering. Thus, for example, in 

 the aquarium red-green, the red crabs go to the 

 red end, the green crabs toward the green one." 



It is interesting to note that the instinct is 

 not connected with sight except so far as the 

 selection of colors is concerned. This was easi- 

 ly proved by blinding the crabs by cutting the 

 optic nerves. After this operation "they dis- 

 guise themselves at once and in quite a normal 

 manner without, however, any reference to the 

 color of the surroundings." Even after the re- 

 moval of the brain the instinct persists, and, "if 

 the crab hapj^ens to touch with its claws a piece 

 of paper or alga, it is often seen to disguise it- 

 self, executing the whole series of movements 

 without omitting any, and in the same order as 

 when in the normal condition." 



This instinct for decoration parallels in a very 

 interesting manner the color protection observed 

 in certain fishes (see, for example, the interest- 

 ing experiments described by Dr. F. B. Sum- 

 mer in the Bulletin for November, 1910, 

 tliough the means as well as the mechanism in- 

 volved are totally different. 



The spider crabs are scavengers and are not 

 used for food, though thej' may be used as bait. 

 They are frequently taken in lobster-pots where 

 they make themselves a nuisance to the lobster 

 fishermen by devouring the bait. The writer 

 recalls seeing more than a hundred Libinias 

 taken from two lobster-pots set overnight in 

 Buzzards Bay by Mr. Vinal Edwards, the vet- 

 eran collector of the Woods Hole Fisheries 

 Station. R. C. Osburn. 



