Part 4

A young Octopus in the Naples aquarium was seen by Schneider to attack a Hermit-crab living within a shell upon which were several Sea-anemones. Upon approaching the Crab the Octopus was stung by the Anemones and quickly retreated. Thereafter it avoided contact with the Crab. It had learned by experience that Anemone-protected Hermit-crabs are “good things to let alone.” In the course of time, however, Octopi learn to extract the Crabs from their shells without being stung by the nettling cells of the Anemones. They also learn to capture large Crabs and Lobsters without getting pinched.

FOOTNOTES:

Romanes, C. J., “Animal Intelligence,” 8th Ed., Page 29, 1904.

CRUSTACEA

Romanes finds in the Arthropoda evidences not only of intelligence, but also (in the Crustacea) of reasoning. Bethe, on the other hand, denies that either associative memory or consciousness exists in any of the Arthropoda (Crabs, Spiders, Insects, etc.) The admittedly complex behavior of these forms is ascribed by Bethe entirely to “reflex action,” wholly devoid of psychic elements.

“This opinion,” says Holmes, “is in part based on a priori deductions from the organization of the nervous system and it is held to chiefly by morphologists and physiologists whose observation of the behavior of animals is limited and warped by preconceptions.” Bethe’s experiments were “obviously inadequate.” As Loeb facetiously puts it, “his conclusions are based upon a few spankings he gave a Crab which obdurately rushed into a dark corner (its instinctive action when frightened) despite the presence there of a Devil-fish (Edolene), the Crab’s natural enemy.”

Yerkes and Huggins, Cowles and other observers have found that Crabs and Crayfish are both capable of learning by experience; while Spaulding has demonstrated the capacity of Hermit-crabs (Pagurus longicarpus) to form associations.

HERMIT-CRABS

The Hermit-crab deliberately seeks a partner-Anemone if one has not chanced to attach itself to its adopted shell-home. Grasping an Anemone with its claw, it places it upon the back of the Mollusk (e.g., Periwinkle, Whelk) shell which it had appropriated for its residence, and then adds a second and a third Anemone until it is completely “camouflaged.” If the Crustacean has occasion to remove to a new shell (which it does after each moult), it sometimes carries a partner-Anemone on its great claw, as a form of protection. The Anemone is, indeed, a sort of outer defense, being richly endowed with batteries of stinging cells. Thomson remarks that the Hermit-crab’s behavior is “suffused with an appreciative awareness of what he is doing.”

Recent experiments conducted by Mr. S. Mikhailoff, of the Oceanographic Institute at Monaco, on the Hermit-crab proved conclusively that a complex neuro-psychical activity in animals having neither a cerebrum nor a central nervous system is possible. The animal was able to distinguish differences in shades of red, “refusing to respond to anything except the color which was the ‘educating’ stimulus, even when shades of red very near this were employed.” In Man the power to distinguish between colors and their shades is located in the gray matter of the cerebrum. The Hermit-crab has no cerebrum.

An important conclusion derived by Mr. Mikhailoff from his extensive experiments is that it is a mistake to compare the ganglionic nervous system of invertebrate animals to the sympathetic system of vertebrate animals. He also proved by the experiments in question that it is possible to establish an associated reflex “in response to any external stimulus whatever.”

It is interesting to note in this connection that Crabs, like Birds and other animals, have their own peculiar homing instincts. Carry a shore-crab back from the beach, lay it down, and unerringly it starts back in the right direction, straight for the sea.

“Some land-crabs of the West Indies and North America combine in large swarms to travel to the sea and to deposit therein their spawn; and each such migration implies concert, co-operation and mutual support,” remarks P. A. Kropotkin (“Mutual Aid,” 1902).

FOOTNOTES:

A resume of Mikhailoff’s experiments, translated from the Revue Général de Science (Paris), January 15, 1921, may be found in The Scientific American for April, 1921. Cf. Morgan, C. L., “Animal Behavior,” 1900.

HORSESHOE CRABS (LIMULUS)

In reference to Horseshoe-crabs Kropotkin says: “I was struck (in 1882, at the Brighton Aquarium) with the extent of mutual assistance which these clumsy animals are capable of bestowing upon a comrade in case of need. One of them had fallen upon its back in a corner of the tank, and its heavy saucepan-like carapace prevented it from returning to its natural position, the more so as there was in the corner an iron bar which rendered the task still more difficult. Its comrades came to the rescue, and for one hour’s time I watched how they endeavored to help their fellow-prisoner. They came two at once, pushed their friend from beneath, and after strenuous efforts succeeded in lifting it upright: but the iron bar would prevent them from achieving the work of rescue, and the Crab would again heavily fall upon its back. After many attempts, one of the helpers would go in the depth of the tank and bring two other Crabs, which would begin with fresh forces the same pushing and lifting of their helpless comrade. We stayed in the Aquarium for more than two hours, and, when leaving, we again came to cast a glance upon the tank: the work of rescue still continued! Since I saw that, I cannot refuse credit to the observation quoted by Dr. Erasmus Darwin--namely, that ‘the common Crab during the moulting season stations as sentinel an unmoulted or hard-shelled individual to prevent marine enemies from injuring moulted individuals in their unprotected state’.”

SPIDERS AND INSECTS

Manifestations of intelligence are much more numerous among Insects and Spiders than in the Crustacea and Mollusca. Forel goes so far as to attribute to Insects an “ability to instinctively draw inferences from analogy.”

FOOTNOTES:

Forel, A., “The Senses of Insects,” (Translation) London, 1908.

SPIDERS

Macfarland places the Spiders as following the Cephalopoda in order of intelligence, as does Sir A. E. Shipley. Says the latter:--

“The Arachnida, together with the Crustacea, Insects, Myriapods, and Peripatus, make up the great phylum Arthropoda, a phylum which, from the point of view of numbers of species and individuals, is the dominant one on this planet, and from the point of view of intelligence and power of co-operating in the formation of social communities is surpassed but by the Vertebrata.”

Spiders possess considerable skill as weavers, hunters, miners, builders and aeronauts. Lacking ears, they “feel” sounds. With but limited visual powers, they nevertheless unerringly pick out the particular strand of the web in which a victim Insect has been trapped. It has been said that the Spider must run to the center of the web before she can know which strand to follow out and reach the entrapped victim. Says Gustav Kafka, in his “Animal Psychology,” “Spiders seem to be endowed with a very keen sense of touch, and know instantly along which strand of their web to go in order to get to any Insect or other object that may become caught in their trap.” The layman probably will wonder why the Spider does not take the shortest path to get its quarry, instead of first going to the center of the web, which involves covering a double distance, perhaps on the very next strand of silk. This is probably due to the Spider’s very limited eyesight, in spite of the six to eight eyes which it possesses--so limited, in fact, that it can see ordinarily for a distance of only a few inches.

Nature has provided the spider with an unusually sharp sense of touch, and it can tell, by the vibration of the connecting strand of silk, that some object has lighted on the web. It speeds to the center of the web, from which, by means of its eight legs and this keen sense of touch it can immediately ascertain by the vibration on which radiating strand the object may have alighted. “That is why all Spiders go first to the center of their web to catch a captive that may lie on the outer radius of the web, and that they may even have passed on the way to the center.”

One cannot but admire, says Prof. E. L. Bouvier, “the marvelous vertical orb-web made by those gifted Spiders which are called indifferently Acaneus or Epeira. Radii spaced at equal distances form the framework and connect it with the helix where Insects are captured and which adheres tenaciously to the radii. From the center where the latter converge there starts a guide-line which connects them with the ordinary retreat of the animal. Lurking at its post with one hand, so to speak, upon the guide-line, the Spider perceives the slightest tremor of the web. Has an Insect been caught in the net? If so, it runs down the guide-line until it reaches it, binds it fast, and slowly sucks its sweet juices, on the spot if it is small, but on its retreat if it is strong.”

The sense of touch is developed in Spiders beyond all comparison with other animals. “A female orb-weaver, at the center of her web, can tell friend from foe, male from female of her species, an Insect suitable for food from one not suitable, an Insect of a certain size from an inanimate object of the same size, and she can also distinguish between sizes of any two objects which happen to fly or be thrown into her web. This is all accomplished by touch vibrations passing along the radii of the orb on which the eyes of the female Spider rest. Moreover, during courtship of Spiders this system of touch vibrations is utilized as a means of signals to inform the male concerning the proper mood of the female for mating--but pity the dwarfed male should he misinterpret her signals, for instantly she pounces upon him and devours him without showing the least mercy.”