specimens. The dearth of such collections, both of ants and of all

other groups of insects, excepting, perhaps, the Coleoptera and Lepi-

doptera, has not ceased to be a great drawback to the study of ento-

mology in America.

The bibliography (Appendix E), which has been carried down to

the close of the year 1908, is unfortunately very voluminous and includes
many titles of unimportant works. Like all such compilations, it is
necessarily incomplete, and undoubtedly contains positive errors. A
serious attempt has been made, however, to reduce these to a minimum,
and I shall be glad to receive any additions or corrections.

For portions of the text and many of the figures I have drawn

rather freely on my previously published papers. A few entire chap-

ters, in fact, such as those on polymorphism, have been reproduced

with only slight verbal alterations. Others, like Chapters XVIII and

XX, are abridgments of longer accounts of the fungus-growing and

honey ants recently published in the Bulletin of the American Museum

of Natural History.

I am under lasting obligations to Professor H. C. Bumpus for the

interest he has shown in the progress of my work, and the aid which

I received in its prosecution while I was Curator of Invertebrate

Zoology in the American Museum of Natural History. To Mr. Roy

W. Miner, Assistant Curator of Invertebrate Zoology in that institu-

tion, I am deeply indebted for much assistance in making out the table

of contents, and especially in arranging and verifying the bibliography.

Many of the illustrations have been made by Miss Ruth B. Howe.

My friend, Professor Oliver S. Strong, of Columbia University, has

most generously permitted me to use a number of the remarkable

photographs which he and Mr. J. G. Hubbard took of living colonies

of various ants in the possession of Miss Adele M. Fielde. Three of

my former pupils, Messrs. A. L. Melander, C. T. Brues and C. G.

Hartman, have also contributed several interesting figures, and Mr.

Brues has aided me in reading the proof.

BUSSEY INSTITUTION,

FOREST HILLS, BOSTON, MASS.,

October 30, 1909.

TABLE OF CONTENTS.

PAGE

I

2

345

CHAPTER I.

ANTS AS DOMINANT INSECTS.

I. The Social Insects, and Their Interest for Man...

II. The Dominance of Ants, as shown by-

1. Unusual Variability. 2. Wide Distribution. 3. Numerical

Ascendancy. 4. Longevity. 5. Abandonment of Detrimental

Specialization. 6. Versatility of Their Relations with Plants

and Other Animals..

III. Probable Cause of the Dominance of Ants..

IV. Correlative Indications of This Dominance..

V. Comparison of Human and Ant Societies..

1. Striking Character of the Resemblances and Their Signifi-

cance. 2. Parallelism in Development. 3. Differences in

Organization.

VI. Analogy between the Ant Colony and the Cellular Organism

VII. Economic Importance of Ants..

1. Their Beneficial Activities. 2. Their Noxious Habits.

VIII. Ants as Objects of Biological Study.

CHAPTER II.

THE EXTERNAL STRUCTURE OF ANTS.

1. The Thorax in General. 2. The Thoracic Elements. 3.

The Stigmata. 4. Comparison of Thoracic Characters of

Male, Female and Worker. 5. The Legs. 6. The Wings.

20

VI. The Abdomen

1. The Various Subfamilies Compared.

2. The Visible Seg-

ments. 3. The Terminal Segments of Female and Worker.

4. The Terminal Segments of the Male.

CHAPTER III.

PAGE

26

III. The Reproductive Organs, Poison Apparatus and Repug-

natorial Organs

39

IV. The Circulatory System, Fat-body, Enocytes, etc.

46

1. Its Segmentation.

51

52

2. Its Finer Structure and the Signifi-

cance of the Pedunculate Bodies.

III. The Ventral Nerve-cord ..

IV. The Sympathetic Nervous System.

V. The Sense-organs

1. Tactile Sensillæ. 2. Olfactory and Gustatory Sensillæ.

3. Chordotonal Organs. 4. The Johnstonian Organ. 5.

The Campaniform Sensillæ. 6. The Lateral Eyes. 7. The

Median Eyes, Stemmata, or Ocelli.

CHAPTER V.

THE DEVELOPMENT OF ANTS.

I. Behavior of Ants toward Their Young Contrasted with

That of Other Hymenoptera

II. The Nursing of the Brood

III. The Egg

PAGE

70

1. Description. 2. Fertilization and Its Relation to Sex.

Development.

IV. The Larva

I. Description. 2. Feeding. 3. Internal Structure.

V. Pupation

VI. Coloration of the Callows

3.

72

76

79

II. Extent and Character of Polymorphism among Insects.... 87

III. The Phylogenetic Origin and Development of Polymor-

phism in Hymenoptera

1. The Views of Various Authors. 2. Phylogeny of the Phases

Known among Ants.

IV. The Development of the Worker the Real Problem of Poly-

morphism in Ants....

90

91

i. Weismann's Theory of Predetermining Units. 2. Spencer's

Theory of Trophic Epigenesis. 3. Emery's Theory of Pre-

disposition.

V. The Three Aspects of the Problem

102

1. The Physiological and Ontogenic. 2. The Ethological and

Phylogenetic. 3. The Psychological.

VI. The Physiological and Ontogenic Method of Explaining the
Development of the Worker

1. The Advantage of the Physiological over the Embryological
Method. 2. The Two General Objections to the Physiolog-
ical Explanation. 3. Inferences which tend to show that
Qualitative Feeding is not Responsible for the Worker Type.
4. The Relation of Underfeeding to the Ontogeny of the
Worker and Related Types. 5. Conclusion.

103