II. Material.
The first observations were made in January of the present year on some material prepared by Professor McClung, to whom I wish here to make most grateful acknowledgment for proposing the line of investigation, and for many helpful suggestions during the progress of the same. The testes were those of adult insects, and showed mostly only mature or almost mature spermatozoa. Enough spermatids were seen to indicate that their transformation into spermatozoa was somewhat peculiar.
The material for the drawings was taken from specimens collected under stones and boards on and near the University campus, at Lawrence, Kan. Young nymphs of Gryllus were caught as early as March 1, but the cells of the testes were all in the spermatogonia and spermatocyte stages. During the early part of May, after the nymphs had passed their third molt, crickets were secured whose testes showed all stages of development and transformation.
Gryllus assimilis, the common black field cricket, has paired testes lying in the anterior dorsal part of the abdomen. These have a whitish transparent appearance, which becomes duller in the adult, showing sometimes a slight yellowish tinge. The shape of each is that of a somewhat conically rounded body, not unlike a flattened strawberry. Each testis consists of a central rachis about 3 mm. long, from which extend a large number of curved follicles varying in length from 1 to 3 mm.
The follicles are larger toward the blind end and taper toward the rachis. Each follicle is divided into cysts, but more often transversely than longitudinally, for frequently one cyst occupies the whole follicle in cross-section. The cysts toward the rachis end of the follicle are much longer and narrower than those of the blind end. The cells are not very large and contain twenty-four chromosomes in the spermatogonial generations; eleven and twelve were most frequently found after the reduction.
The follicles of the cricket testis show the different cell generations and the same relative arrangement of them as McClung (’00) found in Hippiscus, and Sutton (’00) in Brachystola. The spermatogonia are nearest the blind end of the follicles, spermatocytes next, and the spermatids following the latter. The cells of a cyst are not, as in Anasa (Paulmier, ’99), “in the same stage of development,” but only approximately so, for some cysts show cells in the metaphase, while others have reached the telophase. Successive cysts, as in Brachystola, do not show successive stages; for, frequently, growing spermatocytes and late spermatids, or even young spermatozoa, were observed side by side. The individual cells in division pass through prophases, metaphases, anaphases, and telophases—these terms being used according to their usually accepted meanings. (See McClung, ’00.) In this paper I shall begin with the cell when it has reached the telophase of the second spermatocyte division; that is, just after the chromosomes have reached the poles of the spindle.