86 bulletin: museum of comparative zoology. 



one in type Ci. Furthermore the prominent chromomere near the 

 polar granules does not seem to be present, except possibly at vi (fig. 

 107). On the other hand the smaller eonjugant resembles those in 0% 

 in size and otherwise except for the prominent granule already men- 

 tioned. We might therefore be led to suppose that the smaller com- 

 ponent in Cs is homologous to the smaller one in Ci and the two small 

 ones in Ci. But if the example at h (fig. 107) be regarded, it will be 

 seen that this is a small pair lacking any prominent cliromomere near 

 the polar granules, and might therefore be thought to be homologous 

 with the smaller eonjugant in type Cz, if it be considered different from 

 those in type C2. However, even if the somewhat questionable posi- 

 tion of example h, be disregarded as to homologies, it still must be 

 admitted that we have at least three different types of chromosomes 

 appearing in these examples of tetrad C. I may again point out that 

 there is no chance of making a mistake as to the identity of these 

 elements, for the chromosome-pairs B and C are the smallest pairs in 

 the complex, and the different types of C are mutually exclusive, that 

 is, no two of them are ever found in the same animal. I might further 

 add that all the drawings were carefully outlined with a camera 

 lucida and the details filled in so as to represent as accurately as 

 possible the actual conditions as seen in the microscope. The matter 

 of the possible recombination and redistribution of these different 

 types is discussed on page 121. 



h. The Accessory Chromosome. 



The accessory chromosome has not been made an object of special 

 study here. Since it has been so thoroughly and so frequently de- 

 scribed for orthopteran material, it will suffice to give only a brief 

 account of it in this connection. In the first place, it should be stated 

 that the accessory can be recognized as a distinct chromatic individual 

 at practically every stage from the primary spermatogonia to the 

 spermatid. The fact that it forms a large and faintly staining vesicle 

 or "sac" in all the spermagonia except the last, probably accounts for 

 the occasional statement that it can be first recognized in the telo- 

 phase of the last spermatogonia, where it appears as a condensed mass 

 of chromatin, or a chromatin nucleolus. 



Two points deserve to be emphasized: — (1) The accessory, more 

 than the other chromosomes, maintains an exclusive individuality in 

 nearly all stages. However, it sometimes does become associated 



