Blepharida rhois (Family Chrysomelidæ).
The testes were rather too far advanced when this material was collected and no dividing spermatogonia were present. The growth stages (figs. 131, 132) show a faintly staining spireme and a heterochromosome group similar to that of Odontota, a large and a small chromosome attached to a large plasmosome. The spireme appears to go directly over by condensation and segmentation into the dumb-bell-shaped figures seen in the first maturation spindle (figs. 133, 134), though cross-shaped bivalents occasionally occur (fig. 135). The heterochromosome pair, slightly separated by plasmosome material, is usually found at the periphery of the plate (figs. 133-136). Figure 137 is an exceptional anaphase in which the heterochromosome elements are not mingled with the polar masses of chromatin. Figures 138 a and b are equatorial plates of the second mitosis, and figures 139 and 140 are pairs of daughter plates from second spermatocytes showing again the dimorphism of the spermatozoa as to their chromatin content. As in several of the forms studied, material was collected for examination of the somatic cells, but no favorable cases of mitosis were to be found.
Silpha americana (Family Silphidæ).
Only one male of this species was secured, but the large testes gave all stages in abundance. The chromosomes, however, were very small and too numerous, 40 in the spermatogonia (fig. 141). The small chromosome is, nevertheless clearly distinguished in many of these plates (s). The resting spermatogonium contains one very large plasmosome and often one or two smaller ones (fig. 142, p). The unequal pair is seen in the growth stages (figs. 143, 144), and may frequently be seen outside of the equatorial plate of the first spermatocyte spindle (fig. 146). In favorable sections it may also be found in the plate among the other bivalents (fig. 147). Figure 145 is a prophase showing the bivalent chromosomes still connected by linin fibers. An equatorial plate of the first division is shown in figure 148, and a pair of corresponding plates of the second spermatocyte in figure 149. The small heterochromosome divides in the second spindle in advance of the others as seen in figure 150. Therefore, although this form is not especially favorable for detailed study on account of the large number of small chromosomes, the conditions are evidently the same as in the other species described—an unsymmetrical heterochromosome bivalent in the first spermatocyte, giving rise by the second maturation division to equal numbers of dimorphic spermatozoa, one class receiving the large heterochromosome, the other class the small one.
Doryphora decemlineata (Family Chrysomelidæ).
Doryphora decemlineata has been the most difficult one of the collection to work out satisfactorily. The chromosomes in the spermatogonial plates were in most cases much tangled, and the behavior of the heterochromosome pair was such as to suggest an "accessory chromosome" rather than an unequal pair. Abundant material for the study of somatic cells was at hand, but nothing favorable could be found in the sections.
Two spermatogonial plates, containing 36 chromosomes, are shown in figures 151 and 152 (plate XII). The small heterochromosome (s) is slightly elongated. The synizesis and synapsis stages are especially clear. The chromosomes, after the last spermatogonial mitosis go over immediately into a synizesis stage consisting of a polarized group of short loops, which later straighten and unite in pairs (figs. 153 and 154). From these loops are formed the spireme (figs. 155-158), which splits and segments, producing various cross, dumb-bell, and ring forms (figs. 159-163). As in most of the other species of Coleoptera, the unequal pair is not distinguishable until the spireme stage. Figure 162 is an unusual prophase in which all of the equal pairs show a longitudinal split as well as a transverse constriction, and the larger heterochromosome (l) is also split. Figure 163 shows a somewhat later and more common prophase in which the unequal pair, one ring, crosses, and dumb-bells may be seen. This figure, as well as figures 164-168, show the unequal pair in various relations to the other chromosomes. This pair in Doryphora consists of a large V-shaped chromosome with a small spherical one attached to it in different positions. When the small one is behind the V, the group has the appearance of an orthopteran "accessory."
Figures 169-171 show the separation of the two elements outside of the equatorial plate, while in figure 168 the unequal pair is in line with the other chromosomes. In figure 172, an anaphase, the unequal elements are barely separated, while the metakinesis of the other pairs is much further advanced.
Figures 173 and 174 are equatorial plates of the first division, one showing only the larger element of the heterochromosome pair (fig. 174, x), the other both elements (fig. 173, l and s). In the late anaphase (fig. 175) the larger heterochromosome is often seen outside of the polar mass, reminding one again of the "accessory" in the Orthoptera. Occasionally it is found in some other isolated position (fig. 176). Equatorial plates of the second division show the same conditions as in the other species; some contain the larger heterochromosome, others the smaller one (fig. 177, a and b). It was impossible to draw anaphases of the second division from a polar view and the lateral view showed nothing unusual, merely the longitudinal division of all of the chromosomes.
The spermatids show some interesting variations from the other species which have been examined. In figures 178 and 179 we have telophases of the second spermatocyte, showing centrosome and archoplasm (fig. 178) and certain masses of deeply staining material in the cytoplasm (fig. 179, a1). Figures 180 and 181 are young spermatids showing the archoplasm from the second spindle (a2) and a smaller, more deeply staining mass (a1), derived from the irregular masses of the earlier stage (fig. 179, a1). In figures 182 and 183, the axial fiber has appeared and the larger mass of archoplasm (a2) is being transformed into a sheath. The other body remains unchanged. During the following stages this smaller archoplasmic body (a1) lies in close contact with the axial fiber and sheath (a2), and gradually decreases in size (figs. 184-186) until it disappears in a slightly later stage. The acrosome seems to develop directly out of the cytoplasm. The enigmatical body (a1), which is probably archoplasm from the first maturation spindle, as it is not found in the cytoplasm of the first spermatocyte, may serve as nutriment for the developing axial fiber. The sperm head has a peculiar triangular form, staining more deeply on two sides.