Henking finds that the primordial sperm-cells correspond to the primordial ova, both forms of cells in the insect he studied containing the characteristic number of twenty-four chromosomes.
The spermatogenesis of Laphria, according to Cholodkowsky, is very peculiar, and strongly resembles that described by Verson in Bombyx mori. In the blind end of the testicular tubes lies a colossal cell visible to the naked eye, the spermatogone, from which the entire contents of the testes originate. In Bombyx this spermatogone appears in the larva state. Such colossal spermatogones also occur in Lepidoptera of different families (Hyponomeuta, Vanessa, and in the pupa of Chareas graminis), in Trichoptera, and in Hemiptera (Syromastes); and Cholodkowsky inquires whether they may not be typical of insects. Toyama has observed these colossal cells not only in the testes but also in the ovaries of the silkworm. He regards them as supporting cells.
The spermatozoa are inclined to remain in bundles, and in this state are expelled during copulation. These bundles are either root-like, bushy, string-like, sinuous, or worm-like.
Auerbach has observed the spermatozoa of Dyticus marginalis in their passage through the convoluted seminal vesicles. All those arising from one testicular tube are united in a bundle. Each has a very complex structure, bilateral but unsymmetrical. The right side of the head is concave, the left convex; the whole head is longitudinally curved to right or left; and on the posterior half of the right side there is a projecting ridge bearing a hook-shaped cyanophilous “anchor,” at the free end of which an erythrophilous spherule appears. The most remarkable fact is that the spermatozoa unite in pairs in a perfectly definite way, opposed and crossed in a manner somewhat suggestive of a pair of scissors, with the right sides of the heads in contact. During this conjugation, or “dejugation” as Auerbach calls it, the anchors change their shape, and the little spherules are lost. Hundreds of these double spermatozoa are found together in little balls. The conjugation is a temporary one, but it may permit a molecular exchange of substance, perhaps with the result of mixing the hereditary qualities and limiting variability. (Journ. Roy. Micr. Soc., 1893, p. 622.)
In many insects which lack a true penis, the bundle of spermatozoa are united in the ejaculatory duct, forming packets which are enveloped by the secretion of the accessory glands which stiffens into a hard case. These packets are called spermatophores. They are either introduced into the vagina of the female or simply remain outside. Graber has repeatedly observed that the male crickets, in the absence of the female, let their spermatophores fall to the earth; whether it is afterwards made available is not known, because hitherto no case is reported that females seeking impregnation search, as in the case of the Isopod crustacean, Porcellio, for the spermatophores.
In the Gryllidæ and Locustidæ the spermatophore lies in a cup-like cavity under the penis. This is called the “spermatophore cup” (Chadima, 1871), into which the ejaculatory duct of the testis opens.
According to the views of Schneider, the spermatophores, with their capsule, usually consist solely of seminal filaments, which stick closely to each other, and only exceptionally have a capsule formed by a glandular secretion. In Locusta, however, and perhaps also in Gryllus, the sperm is enveloped by the secretion of the accessory glands of the seminal ducts; the spermatophores pass, still fluid, out of the sexual opening of the male into that of the female, but become chilled on the outer surface, so that the sperm, without coming in contact with the air, passes into the receptaculum seminis.
The mode of grouping of the spermatozoa of the Locustidæ as they occur in the spermatheca of the female is remarkable. Their heads lie so close to each other that they form a long shaft, while the numerous threads are arranged so as to look like the two vanes of a feather, the entire mass being like a very long heron’s feather. (Siebold.)
In the honey-bee the spermatophore is likewise enveloped by the secretion of the accessory glands, and thereby becomes a sort of seminal cartridge. This is a peculiar oval body which is carried during the marriage-flight into the air within the upper part of the penis, the so-called penis-bulb. (Leuckart.)