Tanner, Trimen, Ule, Urich, Viehmeyer, Wasmann, Wroughton, and Yung, and in the United States by Buckley, Miss Fielde, Leidy, Lincecum, McCook, Pricer, Mrs. Treat and Turner.

The study of myrmecophily, or the relations of the numerous guests and parasites to the ants, and of the plants frequented by ants, has developed into a very interesting and important branch of ethology which must be mentioned in this connection. An extra

B

D

FIG. 72. Species of Macromischa. (Original.) A and B, Worker of M. isabellæ of Porto Rico; C and D, worker of M. albispina of Culebra.

ordinary number of articles has been published on animal myrmecophily, especially by Wasmann, who since 1886 has devoted himself to this subject with great ardor, and has brought to light many curious facts which have a bearing not only on the ethology of ants but of

many other groups of insects. Other students of this subject are Casey, Donisthorpe, Escherich, von Hagens, Kraatz, Lespes, George Lewis, Lichtenstein, Lucas, Raffray, Reuter, de Saulcey, Joh. Schmidt, Sharp, Trimen, Viehmeyer, and in the United States Cockerell, Brues, Hamilton, Haldemann, King, Schwarz and Wickham. The relation of plants to ants has been studied by many botanists, notably by Delpino, Huth, Holmgren, A. Moeller, Fritz Mueller, Schimper, Treub, von Ihering, Rettig and Ule.

Although the history of ant morphology also goes back to such investigators as Swammerdam and Leuwenhoek, little headway could be made with the study of structure and development in such small organisms till the microscope and the technique of sectioning and staining had been perfected, and this was accomplished only within the last quarter of a century. Forel and Emery, and more. recently Janet, have done very important work on the anatomy of ants. Other authors worthy of mention in this hasty review, are Adlerz, Berlese, Bos, Dewitz. Fenger, Karawaiew, Leydig, Lubbock, Meinert, Nassonow, Pérez and Sharp. As yet American zoologists have accomplished little in this interesting and accessible field of investigation. After this hasty sketch of the history of myrmecology we may take up a somewhat more detailed consideration of the taxonomy of the Formicidæ.

FIG. 73.

Worker of Pristomyr

Inasmuch as the generic and specific characters of ants are to be derived not only from a male and female, but also from a worker caste, the classification of these insects presents certain difficulties and peculiarities not encountered in classifying most other animals. The exact status of a species can, of course, be determined only when all of its phases are known. The worker, as the most abundant, is usually first to fall into the hands of the systematist, and many years may elapse before the corresponding female and male are discovered. There are still a great many exotic and even several European species that are known only from one or at most two of the castes. Moreover, the resemblances between the different phases of the same species are often so remote that it is impossible to correlate workers and females, workers and males, or males and females, unless they have been taken

from the same nests. It is, therefore, largely a matter of convenience that the soldier or worker is selected as the paradigm of the species and takes precedence of the other forms in systematic descriptions. It is obvious that the female, as presenting more numerous and complete characters, would occupy this position, were it not that this caste is, as a rule, less easily obtainable. Except for the same reason, the male would also occupy a more important place in generic and specific diagnosis, since this sex is very stable and often presents important characters, especially in the structure of the genitalia. It is probable, therefore, that at some future time, when large numbers of male and

FIG. 74.

Worker of Myrmicaria brunnea of India. (Bingham.)

female specimens have accumulated in our collections and have been carefully studied, the present classification of the Formicidæ will undergo considerable alteration. Until this time arrives, however, it will be prudent to move slowly in establishing new genera. Mayr, Forel and Emery have all shown admirable conservatism and a laudable absence of the "mihi-itch" in dealing with this aspect of the subject.

Another difficulty arises from the great variability of ants, both among members of the same colony and hence among the progeny of a single or a very few mothers, and among colonies of the same species in different stations or localities. In the former case we have what are known as "nest varieties," in the latter "local or geographical varieties." The danger of basing species on mere nest varieties is often considerable and can be overcome only by studying large series of specimens collected from the same colony. Probably many of the "species" of exotic ants included in our faunistic lists are nothing more than nest varieties. The local varieties are of peculiar interest. Like other animals, certain species of ants may be very stable though widely distributed, others highly variable though very restricted in their range. Some widely distributed species may be stable in some portions of their range and highly variable in others. And finally, some widely distributed species seem to be decidedly variable wherever

they occur. Such a species is Camponotus maculatus, which occurs on every continent and many islands, and varies ad infinitum. In studying such species we are often presented with two sets of variable characters, one of which is adaptive and largely morphological, while the other comprises small indifferent traits of no considerable value to the organism in its struggle with its environment, such as slight peculiarities in size, sculpture, pilosity and color. These characters, which remind one of the De Vriesian "unit characters," are relatively stable in particular races or varieties and have a tendency to combine and recombine in endless permutation. Besides C. maculatus, many of the species of the large genera Formica and Pogonomyrmex are admirable examples of this phe

nomenon.

Characters of importance in classification may be drawn from all parts of the ant's body, but the most useful are furnished by the number of palpal joints, shape of the clypeus, mandibles, shape and comparative length of the antennal joints, shape of the thorax, petiole, postpetiole, spurs of the middle and hind tibiæ, tarsal claws, genitalia of the male, the venation of the wings of both sexes, the structure of the gizzard, larva and pupa. The tribes, genera and species are built on combinations of these characters. But as there are many minor characters, especially in sculpture, pilosity and color, which though constant for all the members of a caste, may nevertheless vary in colonies in different localities, it becomes necessary to recognize smaller divisions than that of the species. These subdivisions are of different rank for the reason that slight differences in form or sculpture are more important, because less variable, than pilosity and coloration. Myrmecologists have therefore recognized two categories within the species, one more important and called the race by Forel, the subspecies by Emery, and another less important category which has been called the variety by both of these authorities. Subspecies may be regarded as small or incipient species in the De Vriesian sense. They are much less frequently connected by transitional forms than the varieties.

The recognition of these various categories necessitates the employment of a quadrinomial nomenclature. Thus one of our common carpenter ants is known as Camponotus herculeanus Linn. subsp. ligniperdus Latreille var. noveboracensis Fitch. This is a strictly North American variety, with red head and thorax, of a smooth race, or subspecies, of the dark-colored, opaque, circumpolar species herculeanus, the typical form of which is confined to Europe. This method of

naming ants has great advantages and some disadvantages. It shows the relationships of the different forms very clearly and this is an admirable trait in nomenclature, but it is also very cumbersome. For ordinary purposes it is sufficient to treat the varietal name as if it were specific and designate the ant mentioned above simply as Camponotus noveboracensis Fitch. This is the more justifiable as the variety among ants is very nearly equivalent to the species among many other groups of animals, such as birds and mammals. In the present work I shall use the binomials as a rule and refer the reader for the full terminology of our North American ants to the catalogue in Appendix C.

This chapter may be concluded with a conspectus of the present classification of the Formicidæ compiled very largely from the works

of Emery and Forel. Concerning the important details of this classification these authorities are unanimous but there are certain points on which they differ, and many which they have left undecided till more material is forthcoming and profounder studies of whole groups of genera have been undertaken. They differ mainly on the limits of two of the five subfamilies, the Ponerinæ and Doryline, Emery maintaining that the tribe Cerapachysii belongs with the Doryline whereas Forel assigns it to the Ponerinæ. The tribe in question certainly possesses peculiarities which ally it with both subfamilies, but the