wall of the cocoon, draw forth the young and strip the enveloping cuticle from its body and appendages. The newly hatched ant which has not yet acquired its deep adult coloration is known as a callow. Owing to the absence of wings, the hatching of the workers is somewhat more easily accomplished than that of the males and females. Dewitz (1878) has shown that the worker larva actually possesses minute histoblasts of these appendages, but they do not develop except in certain abnormal individuals which I have called pterergates (Fig. 63).

In ant larvæ that do not spin cocoons, development and hatching are, of course, considerably simplified (Figs. 48 and 49). In such species the adult larva passes at once to the semipupa stage after discharging the meconium. A worker receives the black pellet in its mandibles, or even pulls it out of the large intestine and deposits it on the refuse heap of the nest. The fact that the cocoon is constantly present in the most primitive ants and as constantly lacking in large groups of highly specialized forms, shows that it is an ancient inheritance from solitary, wasplike ancestors. Certain Camponotine genera and subgenera (Prenolepis, Ecophylla, Plagiolepis and Colobopsis) always have nude pupa, and in certain species of Formica and Lasius the cocoon may be present or absent in the brood of the same colony or even in the male and female pupæ. Janet (1896c) regards the sudden elimination of the envelope in these species as a mutation, or saltatory variation. I have seen the nude pupæ of a Dolichoderine.

ant (Iridomyrmex geinitzi) in the Baltic amber (Lower Oligocene), so that the complete elimination of the cocoon, in this subfamily at

least, is not a very recent development. The shape and color of the cocoon differ considerably in different species. In Leptogenys, for example, it is very long and slender and of a dark-brown color, in Lasius and Formica it is a pale buff or whitish and broadly elliptical, in Ponera pennsylvanica it is oblong and sulphur yellow.

FIG. 45. Camponotus americanus X 2. (Photograph by J. G. Hubbard and Dr. O. S. Strong.) a. Egg: b. young larvæ; c, older larvæ d. worker cocoons; e. female cocoon; f, worker major pupa removed from cocoon: g, worker media in the act of hatching; h, major workers; i, minor workers; k, virgin female; 1, males.

are black, the callows are drab or yellowish (Formica subsericea), while in others they may be orange or deep red (Platythyrea punctata). The callows of bright red ants are often sulphur yellow or orange (Polycrgus, Pogonomyrmex, Myrmica mutica), while in the yellow species, like our North American Lasius of the subgenus Acanthomyops, the callows are sordid white or drab (Fig. 46, a).

(Photograph by J.

FIG. 46. Acanthomyops claviger workers and cocoons, X 2. G. Hubbard and Dr. O. S. Strong.) a, Callow workers; b, queen cocoons; remaining cocoons those of workers.

The length of embryonic, larval and pupal life appears to be highly variable and to depend very intimately on temperature. Wasmann (1891) and Miss Fielde (1905g) have shown that a rise of temperature at once induces both females and workers to lay and accelerates the

growth of the larvæ. According to Miss Fielde: "It appears that the time of development may be altered by a change of the prevailing temperature and that an intervening period of recuperation will be maintained in spite of a temperature stimulus. Other factors being equal, the development of the eggs within the ovaries, the deposit of the eggs, the feeding and growth of the larvæ, the pupation and hatching, all appear to be determined by temperature. The degree of heat suiting the species probably varies for the different stages of development. . . Among the ant-young observed by me, none has developed at a temperature below 70° F., while long exposure to a degree of heat above 90° F. manifestly causes injury." Both Miss Fielde and Janet have taken pains to ascertain the duration of the embryonic, larval and pupal stages. Their results are remarkably similar when we consider that they were made on different species and in different countries. For

b

Aphanogaster fulva Miss Fielde gives the duration of the embryonic period as 17 to 22 days (usually 19 days), that of the larval period as 24 to 27 and the pupal period as 13 to 22 days, while Janet gives as the corresponding periods for Myrmica rubra 23 to 24 days, 30 to 71 days, and 18 to 22 days. This makes the total for the entire development of A. fulva 54 to 141 days and of M. rubra 71 to 117 days. According to Miss Fielde, the parthenogenetic offspring of workers develop much more slowly than the offspring of females. In wild colonies development is most rapid during the spring and summer months, and undoubtedly in many species the larvæ manage to live from November till the following March without showing any signs of development.

α

FIG. 47. Semipupa becoming a pupa. (Pérez.) a, Semipupa, still covered by larval skin; b, larval skin removed from anterior portion of body; c, pupa.

Although the developmental periods above given are unusually long for metabolic insects, the longevity of adult ants is still more remarkable. The male is supposed to be very short-lived and there. can be little doubt that in most species it dies soon after the nuptial flight. Still Lubbock (1894) mentions males of Myrmica ruginodis which lived in an artificial nest from August 14 till the following April, and Janet (1904, p. 40) kept males of M. rubra alive from October 12 till the beginning of April. The males undoubtedly live

ANTS.

FIG. 48. Colony of Aphanogaster picea with naked brood, slightly enlarged. (Photograph by J. G. Hubbard and O. S. Strong.)

b, male.

a, Mother queen of colony;