52 STUDIES IN SPERMATOGENESIS. 



All of the evidence at hand leads to the conclusion that in the 

 Coleoptera, the univalent elements of all the pairs, equal and unequal, 

 separate in the first spermatocyte mitosis and divide quantitatively in 

 the second. In this respect the behavior of the chromosomes in this 

 order appears to be much more uniform than in the Orthoptera and 

 Hemiptera. 



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 Coleop- 

 tera 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 chromo- 

 somes, instead of being delayed, as in many of the Hemiptera heter- 

 optera. 



Aphrophora (Hemiptera homoptera) agrees with the Anasa group of 

 the Hemiptera heteroptera in having a pair of condensed wz-chromo- 

 somes, 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 chromo- 

 some 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 ooctyes. 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 hete- 

 rochromosomes 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 investi- 

 gators will soon throw more light on the heterochromosomes of this 

 order. 



