The element x is, of course, present in only one-half of these nuclei. In the equatorial plate, figure 142, it is absent; in figure 143 it is present, but can not be distinguished from the other chromosomes, while in figure 144 it is rendered conspicuous by its spherical form and isolated position. In only a few cases has it been possible to distinguish x in the spindle. Figures 146 and 147 show two of these cases where this element is clearly double and of different form from the other chromosomes. It is probable that it divides and so goes into one-half of all of the spermatids, as in McClung's typical cases of the accessory chromosome. Figure 145 shows the usual appearance of the other chromosomes in metaphase. The two spermatids of a pair are always alike so far as any evidence of the presence of the element x is concerned (fig. 148). Figure 149 is an exceptional case, where one chromatin element (possibly x) has evidently divided late and been left out in the cytoplasm; a smaller chromatin granule is also present in the cytoplasm of each spermatid. All of the spermatids, as in Stenopelmatus, develop a deeply-staining body, which, however, in this case is usually centrally located and often appears double (figs. 150-152).
The spindle-remains (Spindelreste) forms a very conspicuous body at one side of the nucleus in the spermatids, and occasionally a mass of chromatin, probably due to imperfect mitosis, is found near the spindle-substance (fig. 150). The mass of spindle-substance at first appears structureless, but soon assumes the condition shown in figures 150 to 152. In one individual many of the spermatids had two balls of spindle-material (fig. 152), and the resulting later stages were double-tailed (fig. 153). Figure 156 shows how the spindle-substance goes into the tail and gradually disappears as the tail lengthens.
The centrosome is evidently applied to the nuclear membrane, as in Stenopelmatus, and the middle-piece is developed in connection with it, as in figures 156-157, 154-155, 158-160. The element x of the spermatids gradually disappears (figs. 150, 159). An acrosome develops at the anterior end, the head condenses and lengthens, and we have the ripe spermatozoön (fig. 161). The tail is very long and is shown only in part.
Of the forms studied, Blattella alone has many degenerate spermatozoa. Some follicles have none, others a number varying perhaps from one-fourth to three-fourths of the whole number. No evidence of degeneracy was detected among the young spermatids up to the stage shown in figures 154-155, where a few like figure 162 were found. Most of the degenerate forms occur among the nearly ripe spermatozoa or in the sperm-ducts. Such are shown in figures 163 to 168. The chromatin is strangely broken up into irregular clumps, and probably no two of these degenerate sperm-heads can be found which are alike. The tails are always imperfect. The distribution and varying numbers of these degenerate spermatozoa make it impossible to interpret their condition as due to the absence of the accessory chromosome, as Miss Wallace does in the spider. The only probable explanation, it seems to me, is imperfect mitosis. Cases where more or less chromatin is left behind in the cytoplasm, especially in the first spermatocyte mitosis, are very common, and such cases as those shown in figures 149 and 150 are not rare. The giant cells, so far as I have been able to trace them, do not develop into spermatozoa.
The most important points are:
(1) The presence of the element x in the spermatogonia, closely associated with the nucleolus.
(2) The uneven number of chromatin elements in the metaphase of spermatogonial divisions.
(3) The connection of the element x with the spireme up to the stage where the spireme segments to form the bivalent chromosomes.
(4) The varied character of the tetrads, showing the first spermatocyte division to be a reducing division in the sense that it separates whole chromosomes.
(5) The fact that the element x fails to divide in the first maturation division, does divide in the second, but can not be traced beyond the equatorial plate of the latter mitosis.