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.
III. Observations.
(a) the nucleus.
The chromatin in Gryllus behaves very much as Henking (’91) has described for Pyrrhocoris, and Paulmier (’99) for Anasa. At the end of the anaphase the chromosomes are crowded together at the poles of the spindle. ([Fig. 1.]) A clear space begins to be formed around them, especially on the equatorial side. ([Fig. 2.]) They then separate and are scattered somewhat evenly over the nuclear membrane when it is formed, as seen in [figs. 4, 5, and 6]. Soon protuberances appear on the surface of the individual chromosomes, making their outlines irregular. At about this time they begin to show a granular structure. The chromosomes break up more and more, and soon the chromatin appears in irregularly arranged patches or blotches of granules of various sizes. ([Fig. 8.])
Meanwhile the nucleus has slowly increased in size. It reaches its maximum, which is probably about treble its original diameter, before the cell begins to elongate. The granules have been breaking up into finer and finer pieces, until, a little after the cell has reached its maximum, the chromatin has largely disappeared, or, to be more exact, has lost its affinity for stains. ([Fig. 16.]) As the cell begins to elongate, the nucleus goes to one end, namely, that toward the periphery of the cyst. ([Figs. 14 and 15.]) The chromatin again frequently appears in patches as the cell decreases in size. ([Figs. 33 and 36.]) In many cells the patches never disappear. When it has diminished to less than half its maximum diameter, the nucleus begins to elongate, becoming elliptical, and finally forms the long, tube-like head of the spermatozoon. ([Figs. 43 and 45.])
I found here that the nucleus was hollow, or, better, that it showed a clear space within. For a long time it contains the many chromatin granules, as seen in [figs. 39, 40, and 41]; but at last the walls seem to attract all these granular masses, and the center is entirely clear, as in [fig. 45]. In [fig. 44] are shown cross-sections of spermatozoa heads, of the stage of [fig. 43]. In [fig. 45] we have a mature spermatozoon head.
The accessory chromosome in Gryllus lags behind during the spermatogonial divisions, just as in Xiphidium (McClung, ’99), and retains its identity all through the growth period, in many cases becoming quite large. At first it cannot be distinguished in the spermatid, but soon its stronger stain and exemption from disintegration make it apparent. ([Fig. 4.]) It is flattened against the nuclear wall and, unlike Paulmier’s “small chromosome,” it does not break up but remains intact, as Henking and McClung have described. ([Figs. 14, 18], [32, 37], and others.) It gets larger and then smaller, and is finally lost in the rest of the chromatin, as the latter condenses to form the spermatozoon head. I was not able to see that it occupied one side of the elongating head, as McClung describes it in Xiphidium. The darker stain and regular contour, and sometimes its greater size, made it in most stages quite evident.