the fact that the males of certain species present two forms, differing from each other in the size and length of their jaws; and this reminds us of the above cases of dimorphic crustaceans.

"21

The male is generally much smaller than the female, sometimes to an extraordinary degree,20 and he is forced to be extremely cautious in making his advances, as the female often carries her coyness to a dangerous pitch. De Geer saw a male that "in the "midst of his preparatory caresses was seized by the object of “his attentions, enveloped by her in a web and then devoured, a sight which, as he adds, filled him with horror and indignation.' The Rev. O. P. Cambridge 22 accounts in the following manner for the extreme smallness of the male in the genus Nephila. ́ M. Vinson gives a graphic account of the agile way in which "the diminutive male escapes from the ferocity of the female, by gliding about and playing hide and seek over her body and along her gigantic limbs: in such a pursuit it is evident that "the chances of escape would be in favour of the smallest males, "while the larger ones would fall early victims; thus gradually

66

a diminutive race of males would be selected, until at last they "would dwindle to the smallest possible size compatible with the "exercise of their generative functions,-in fact probably to the "size we now see them, i.e., so small as to be a sort of parasite upon the female, and either beneath her notice, or too agile and "too small for her to catch without great difficulty."

Westring has made the interesting discovery that the males of several species of Theridion have the power of making a stridulating sound, whilst the females are mute. The apparatus consists of a serrated ridge at the base of the abdomen, against which the hard hinder part of the thorax is rubbed; and of this structure not a trace can be detected in the females. It deserves notice that several writers, including the well-known arachnologist Waickenaer, have declared that spiders are attracted by music.2+ From the analogy of the Orthoptera and Homoptera,

20 Aug. Vinson ('Aranéides des Iles de la Reunion,' pl. vi. figs. 1 and 2) gives a good instance of the small size of the male, in Epeira nigra. In this species, as I may add, the male is testaceous and the female black with legs banded with red. Other even more striking cases of inequality in size between the sexes have been recorded (Quarterly Journal of Science,' 1868, July, p. 429); but I have not seen the original accounts.

21 Kirby and Spence, Introduc

to be described in the next chapter, we may feel almost sure that the stridulation serves, as Westring also believes, to call or to excite the female; and this is the first case known to me in the ascending scale of the animal kingdom of sounds emitted for this purpose.

25

Class, Myriapoda.-In neither of the two orders in this clase, the millipedes and centipedes, can I find any well-marked instances of such sexual differences as more particularly concern us. In Glomeris limbuta, however, and perhaps in some few other species, the males differ slightly in colour from the females; but this Glomeris is a highly variable species. In the males of the Diplopoda, the legs belonging either to one of the anterior or of the posterior segments of the body are modified into prehensile hooks which serve to secure the female. In some species of Iulus the tarsi of the male are furnished with membranous suckers for the same purpose. As we shall see when we treat of Insects, it is a much more unusual circumstance, that it is the female in Lithobius, which is furnished with prehensile appendages at the extremity of her body for holding the male.

CHAPTER X.

SECONDARY SEXUAL CHARACTERS OF INSECTS.

Diversified structures possessed by the males for seizing the femalesDifferences between the sexes, of which the meaning is not understoodDifference in size between the sexes- -Thysanura-Diptera-Hemiptera -Homoptera, musical powers possessed by the males alone-Orthoptera, musical instruments of the males, much diversified in structure; pugnacity; colours-Neuroptera, sexual differences in colour-Hyme noptera, pugnacity and colours-Coleoptera, colours; furnished with great horns, apparently as an ornament; battles; stridulating organs generally common to both sexes.

IN the immense class of insects the sexes sometimes differ in their locomotive-organs, and often in their sense-organs, as in the pectinated and beautifully plumose antennæ of the males of many species. In Chloëon, one of the Ephemeræ, the male has great pillared eyes, of which the female is entirely destitute.' The ocelli are absent in the females of certain insects, as in the

Mutillida; and here the females are likewise wingless. But we are chiefly concerned with structures by which one male is enabled to conquer another, either in battle or courtship, through his strength, pugnacity, ornaments, or music. The innumerable contrivances, therefore, by which the male is able to seize the female, may be briefly passed over. Besides the complex structures at the apex of the abdomen, which ought perhaps to be ranked as primary organs," ,2 "it is astonishing," as Mr. B. D. Walsh has remarked, "how many different organs are worked in by nature "for the seemingly insignificant object of enabling the male to grasp the female firmly." The mandibles or jaws are sometimes used for this purpose; thus the male Corydalis cornutus (a neuropterous insect in some degree allied to the Dragon-flies, &c.) has immense curved jaws, many times longer than those of the female; and they are smooth instead of being toothed, so that he is thus enabled to seize her without injury. One of the stag-beetles of North America (Lucanus elaphus) uses his jaws, which are much larger than those of the female, for the same purpose, but probably likewise for fighting. In one of the sand-wasps (Ammophila) the jaws in the two sexes are closely alike, but are used for widely different purposes: the males, as Professor Westwood observes, "are exceedingly ardent, seizing "their partners round the neck with their sickle-shaped jaws;" whilst the females use these organs for burrowing in sand-banks and making their nests.

B

The tarsi of the front-legs are dilated in many male beetles, or are furnished with broad cushions of hairs; and in many genera of water-beetles they are armed with a round flat sucker, so that the male may adhere to the slippery body of the female. It is a

species having been observed in union. Mr. MacLachlan informs me (vide Stett. Ent. Zeitung,' 1867, s. 155) that when several species of Phryganidæ, which present strongly-pronounced differences of this kind, were confined together by Dr. Aug. Meyer, they coupled, and one pair produced fertile ova. 3The Practical Entomologist, Philadelphia, vol. ii. May, 1867 p. 88.

Mr. Walsh, ibid. p. 107.

5 Modern classification of In sects,' vol. ii. 1840, pp. 205, 208 Mr. Walsh, who called my attention to the double use of the jaws, says that he has repeatedly observed this fact.

6

much more unusual circumstance that the female of some waterbeetles (Dytiscus) have their elytra deeply grooved, and in Acilius sulcatus thickly set with hairs, as an aid to the male. The females of some other waterbeetles (Hydroporus) have their elytra punctured for the same purpose. In the male of Crabro cribrarius (fig. 9), it is the tibia which is dilated into a broad horny plate, with minute membraneous dots, giving to it a singular appearance like that of a riddle." In the male of Penthe (a genus of beetles) a few of the middle joints of the antennæ are dilated and furnished on the inferior surface with cushions of hair, exactly like those on the tarsi of the Carabidæ," and obviously for "the same end." In male dragonflies, "the appendages at the tip "of the tail are modified in an "almost infinite variety of curious "patterns to enable them to embrace the neck of the female." Lastly, in the males of many insects, the legs are furnished with peculiar spines, knobs or spurs; or the whole leg is bowed or thickened, but this is by no means invariably a sexual character; or one pair, or all three pairs are elongated, sometimes to an extravagant length.

Fig. 9. Crabro cribratius. Upper figure, male; lower figure, female.

8

The sexes of many species in all the orders present differences, of which the meaning is not understood. One curious case is that of a beetle (fig. 10), the male of which has the left mandible much enlarged; so that the mouth is greatly distorted. In another Carabidous beetle, Eurygnathus, we have the case,

We have here a curious and inexplicable case of dimorphism, for some of the females of four European species of Dytiscus, and of certain species of Hydroporus, have their elytra smooth; and no intermediate gradations between sulcated or punctured, and the quite smooth elytra have been observed. See Dr. H. Schaum, as quoted in the Zoologist,' vol. v.-vi. 1847-48, p. 1896. Also Kirby and Spence,

the

Introduction to Entomology, vol. iii. 1826, p. 305.

7 Westwood, Modern Class.' vol. ii. p. 193. The following statement about Penthe, and others in inverted commas, are taken from Mr. Walsh, Practical Entomologist,' Philadelphia, vol. ii. p. 88.

8 Kirby and Spence, 'Introduct.' &c., vol. iii. pp. 332-336.

20.

Insecta Maderensia,' 1854, p.

unique as far as known to Mr. Wollaston, of the head of the female being much broader and larger, though in a variable degree, than that of the male. Any number of such cases could be given. They abound in the Lepidoptera: one of the most extraordinary is that certain male butterflies have their fore-legs more or less atrophied, with the tibiæ and tarsi reduced to mere rudimentary knobs. The wings, also, in the two sexes often differ in neuration,10 and sometimes considerably in outline, as in the Aricoris epitus, which was shewn to me in the British Museum by Mr. A. Butler. The males of certain South American butterflies have tufts of hair on the margins of the wings, and horny excrescences on the discs of the posterior pair." In several British butterflies, as shewn by Mr. Wonfor, the males alone are in parts clothed with peculiar scales.

The use of the bright light of the female glow-worm has been subject to much discussion. The male is feebly luminous, as are the larvæ and even the eggs. It has been supposed by some authors that the light serves to frighten away enemies, and by others to guide the male to the female. At last, Mr. Belt 12 appears to have solved the difficulty: he finds that all the Lampyride which he has tried are highly distasteful to insectivorous mammals and birds. Hence it is in accordance with Mr. Bates' view, hereafter to be explained, that many insects mimic the Lampyrida closely, in order to be mistaken for them, and thus to escape destruction. He further believes that the luminous species profit by being at once recognised as unpalatable. It is probable that the same explanation may be

10 E. Doubleday, Annals and Mag. of Nat. Hist.' vol. i. 1848, p. 379. I may add that the wings in certain Hymenoptera (see Shuckard, Fossorial Hymenop.' 1837, pp. 3943) differ in neuration according to

sex.

11 H. W. Bates, in Journal of Proc. Linn. Soc.' vol. vi. 1862, p.

Fig. 10. Taphroderes

distort us (much enlarged). Upper figure, male; lower figure, female. extended to the

74. Mr. Wonfor's observations are quoted in Popular Science Review,' 1868, p. 343.

12 The Naturalist in Nicaragua,' 1874, pp. 316-320. On the phosphorescence of the eggs, see Annals and Mag. of Nat. Hist.' 1871,' Nov., p. 372.