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remain with comparatively little change throughout the winter. It is much more difficult to ascertain the length of life of the perfect insect, on account of their gregarious habits, and the difficulty of recognising individual ants. I have found, however, as we shall presently see, that their life is much longer than has been generally supposed.
It is generally stated in entomological works that the males of ants die almost immediately. No doubt this is generally the case. At the same time, some males of Myrmica ruginodis, which I isolated with their mates in August 1876, lived until the following spring; one of them till May 17.
It has also been the general opinion that the females lived about a year. Christ' indeed thought they might last three or even four seasons, but this was merely a suggestion, and Forel expressed the general opinion when he said, "Je suis persuadé qu'en automne il ne reste presque plus que les ouvrières écloses pendant le courant de l'été.' life of a queen is also, he thinks, not more than twelve months. I have found, however, that the life of the queens and workers is much longer than had been supposed. I shall give further details in a subsequent chapter, but I may just mention here that I have now (August 1882) two queens which have lived with me since the year 1874. They must therefore be at least eight years old, and seem still quite strong and
· Naturgeschichte der Insekten.
well. They continue still (1882) to lay a few eggs, which, I may add, produce workers.
I have also some workers which I have had since 1875.
The body of an ant consists of three parts: the bead, thorax, and abdomen. The head bears the principal organs of sense, and contains the brain, as the anterior portion of the nervous system may fairly be called. The thorax, supporting the legs and, when they are present, the wings, contains the principal muscles of locomotion. The abdomen contains the stomach and intestines, the organs of reproduction, the sting, &c.
Returning to the head : the antennæ consist of a short spherical basal piece, a long shaft, known as the scape, and a flagellum of from six to seventeen (geuerally, however, from ten to thirteen) short segments, the apical ones sometimes forming a sort of club. The number of segments is generally different in the males and females.
The eyes are of two kinds. Large compound eyes, one on each side of the head ; and ocelli, or so-called simple eyes. The compound eyes consist of many facets. The number differs greatly in different species, and in the different sexes, the males generally having the greatest number. Thus, in Formica pratensis there are, according to Forel, in the males about 1,200 in each eye, in the fertile females between 800 and 900, in the workers about 600. Where the workers vary in size
Having reference to the facts stated on page 37, this is a result of great physiological interest.
they differ also in the number of facets. Thus, again following the same authority, the large workers of Camponotus ligniperdus have 500, the smaller ones only 450; while in the Harvesting ant (Atta barbara) the contrast is even greater, the large specimens having 230, the small ones only from 80 to 90. The ordinary workers have in Polyergus rufescens about 400; in Lasius fuliginosus, 200; in Tapinoma erraticum, 100; in Plagiolepis pygmæd, 70 to 80; in Lasius flavus, about 80; in Bothriomyrmex meridionalis,55; in Strongylognathus testaceus, Stenamma Westwoodii, and Tetramorium cæspitum, about 45 ; in Pheidole pallidula, about 30; Myrmecina Latreillei, 15; Solenopsis fugax, 6 to 9; while in Ponera contracta there are only from 1 to 5; in Eciton only 1;
; and in Typhlopone the eyes are altogether wanting.
The number of facets seems to increase rather with the size of the insect than with the power of vision.
The ocelli are never more than three in number, disposed in a triangle with the apex in front. Sometimes the anterior ocellus alone is present.
In some species the workers are altogether without ocelli, which, however, are always present in the queens and in the males.
The mouth parts are the labrum, or upper lip; the first pair of jaws or mandibles; the second pair of jaws or maxillæ, which are provided with a pair of palpi, or feelers; and the lower lip, or labium, also bearing
; a pair of palpi.
The thorax is generally considered to consist, as in other insects, of three divisions—the prothorax, mesothorax, and metathorax. I have elsewhere, however, given reasons into which I will not at this moment enter, for considering that the first abdominal segment has in this group coalesced with the thorax. The thorax bears three pairs of legs, consisting of a coxa, trochanter, femur, tibia and tarsus, the latter composed of five segments and terminating in a pair of strong claws.
In the males and females the meso- and metathorax each bear a pair of wings, which, however, in the case of the female, are stripped off by the insects themselves soon after the marriage flight.
The workers never possess wings, nor do they show even a rudimentary representative of these organs. Dr. Dewitz has, however, pointed out that the full-grown larvæ of the workers possess well-developed 'imaginal disks,' like those which, in the males and females, develope into the wings. These disks, during the pupal life, gradually become atrophied, until in the perfect insects they are represented only by two strongly chitinised points lying under the large middle thoracic spiracles. No one unacquainted with the original history of these points would ever suspect them to be the rudimentary remnants of ancestral wings.
The thorax also bears three pairs of spiracles, or breathing holes.
· Zeit. f. wiss. Zool., vol. xxviii. p. 555.
The abdomen consists of six segments, in the queens and workers, that is to say in the females, and seven in the males. In the Formicidæ the first segment, as a general rule, forms a sort of peduncle (known as the scale or knot) between the metathorax and the remainder of the abdomen. In the Myrmicidæ two segments are thus detached from the rest.
The Poneridæ form, as regards the peduncle, and in some other respects, an intermediate group between the Formicidæ and the Myrmicidæ. The second abdominal segment is contracted posteriorly, but not so much so as to form a distinct knot.
The form of the knot offers in many cases valuable specific characters.
I am disposed to correlate the existence of a second knot among the Myrmicidæ with their power of stinging, which is wanting in the Formicidæ. Though the principal mobility of the abdomen is given in the former, as in the latter, by the joint between the metathorax and the knot, still the second segment of the peduncle must increase the flexibility, which would seem to be a special advantage to those species which have a sting. It must indeed be admitted that Ecophylla' has a sting, and yet only one knot; but this, of course, does not altogether negative my suggestion, which, however, I only throw out for consideration,
1 Proc. Linn. Soc., vol. v. p. 101.