COMPARISON OF THE COLEOPTERA WITH THE HEMIPTERA AND LEPIDOPTERA.
As has been seen above, the conditions in the Coleoptera, so far as the heterochromosomes are concerned, correspond very closely in final results with those in the Hemiptera heteroptera and the Orthoptera. In minor details these chromosomes are less peculiar in the Coleoptera than in either of the other orders. Even condensation during the growth stage is not universal, and synapsis of the heterochromosomes apparently occurs simultaneously with that of the ordinary chromosomes, instead of being delayed, as in many of the Hemiptera heteroptera.
Aphrophora (Hemiptera homoptera) agrees with the Anasa group of the Hemiptera heteroptera in having a pair of condensed m-chromosomes, in the growth stage, but this pair is already united in synapsis when first seen. It differs from Anasa, but agrees with Banasa and Archimerus in exhibiting a typical odd chromosome which goes to one pole without division in the first spermatocyte, and divides with the other chromosomes in the second spermatocyte. The odd chromosome in this species of Hemiptera, therefore, behaves like that in the Coleoptera and Orthoptera. The most interesting points in the results of this study of the germ cells of Aphrophora is the discovery of two pairs of condensed chromosomes in certain phases of the growth stages of the oöcytes. This has not been shown to be the case in any other species of Hemiptera, so far as I can ascertain. It is now evident that in the Heteroptera homoptera there are at least two distinct classes as to behavior of chromosomes. In one class we have the Aphids (Stevens, '05 and '06) and Phylloxera (Morgan, '06) in which no heterochromosomes have been found, while in the other class are such forms as Aphrophora with both a pair of m-chromosomes and a typical odd heterochromosome.
The two species of Lepidoptera examined indicate that here we may have conditions comparable to those in Nezara—an equal pair of heterochromosomes whose only apparent peculiarity is their condensed form during the growth stage. Doubtless the results of other investigators will soon throw more light on the heterochromosomes of this order.