Miscellaneous Coleoptera.
Considerable material from the spruce borers was collected at Harpswell, Maine, but the species were not identified. Although these insects were in the pupa stage, most of the testes were too old. There were no dividing spermatogonia and few spermatocyte mitoses. Most of the spermatocytes contained 10 chromosomes, one of which was plainly an unequal pair. In a few testes the number was 11, indicating that pupæ of two species had been collected. Figure 187 shows the metaphase of first spermatocyte mitosis with the unequal pair in metakinesis. Figures 188 and 189 are first spermatocyte equatorial plates of the two species, containing 10 and 11 chromosomes respectively. Figure 190 is a first spermatocyte spindle in anaphase, showing the unequal pair behind the other chromosomes. Figure 191 is an equatorial plate from a second spermatocyte, showing the small chromosome. In figure 192 are shown several of the bivalent chromosomes, including the unsymmetrical pair, from nuclear prophases of the first division, all from the same cyst.
Adalia bipunctata (family Coccinellidæ), the common lady beetle, has a very conspicuous pair of unequal heterochromosomes, as may be seen in figures 193-197 (plate XIII). This would seem to be a favorable form for determining the chromosome conditions in somatic cells, but no clear equatorial plates were found in either larvæ or pupæ.
In Cicindela primeriana (family Cicindelidæ) there are 18 chromosomes in the spermatogonium (fig. 198), one being small. The heterochromosome group is blended into a vacuolated sphere in growth stages (figs. 199, 200). In the metaphase of the first division it is trilobed, or tripartite (fig. 201), and in metakinesis, a small spherical chromosome separates from a much larger V-shaped one (fig. 202). Equatorial plates of first and second spermatocytes are shown in figures 203 and 204. Whole cysts of giant first spermatocytes were found both in growth stages (fig. 205) and prophases (fig. 206). Here the heterochromosome group is plainly double (fig. 205), and the conditions observed must have been due to the failure of a spermatogonial mitosis to complete itself.
Several of the Carabidæ have been studied, and the material, though not especially favorable, is interesting in that some members of the family have an unequal pair of heterochromosomes, others an odd one. Chlænius æstivus (figs. 207-212), Chlænius pennsylvanicus (figs. 213-215), and Galerita bicolor (fig. 216) have the unequal pair, while Anomoglossus emarginatus (figs. 217-223) has an odd heterochromosome (x), which behaves exactly like the larger heterochromosome in other carabs.
In the Elateridæ and Lampyridæ we also have examples of the second type with the odd chromosome. Two Elaters, species not determined (figs. 224-229 and 230-235), have each 19 chromosomes in the spermatogonia (figs. 224 and 230), and in the first spermatocyte division an odd chromosome (x) which is in each case the smallest. In the first of these Elaters, the female somatic number was determined to be 20 (fig. 229). In the second Elater the pairs of second spermatocytes, containing 9 and 10 chromosomes respectively in the two cells, were in nearly every case connected as shown in figure 235, one pair of chromosomes not having separated completely in the first mitosis. Of Ellychnia corrusca (family Lampyridæ) only the spermatogonial equatorial plate, containing 19 chromosomes (x, the odd one) is given, as no material in maturation has yet been obtained, and a comparative study of the germ cells of the Elateridæ and Lampyridæ will be made as soon as suitable material can be secured.
In addition to the species of Coleoptera described here, two others, Coptocycla aurichalcea and Coptocycla guttata have been studied by one of my students and the results published elsewhere (Nowlin, '06). In both an even number of chromosomes (22, 18) was found in the spermatogonia, one being very small and forming with a larger one an unequal pair which remained condensed during the growth stage and separated into its larger and smaller components in the first spermatocyte mitosis. The result of maturation, as in the other species here described and in Tenebrio molitor, is dimorphism of the spermatozoa. The method of synapsis in Coptocycla is like that described for Chelymorpha argus.