140 bulletin: museum of comparative zoology. 



without attempting any specific statement. McClung (:01), Stevens 

 (:05'\ :06^) and "Wilson (:06) have pointed out the possible signifi- 

 cance of the allosomes in sex determination, so that it is unnecessary 

 to take up this subject, especially since in the present state of our 

 knowledge it can only lead to fruitless theorizing. I think it must be 

 conceded that we have at present no satisfactory explanation of either 

 the origin or function of the allosomes, and until we know more about 

 these interesting elements, especially during oogenesis and fertilization 

 it is idle to speculate further on the subject. 



6. The Individuality of the Chromosomes. 



The theory of the individuality of the chromosomes, which was 

 first formulated by Rabl ('85) and later ardently advocated by Boveri, 

 has in recent years received strong support, especially from writers 

 on insect spermatogenesis. The constant recurrence in successive 

 generations of the autosome pairs, which are so clearly marked in 

 these forms, is very difficult to explain on any other view. When 

 we consider that each species is characterized by a fixed number of 

 symmetrically paired autosomes which possess definite form and size 

 relations, it is almost impossible to escape the conclusion that we are 

 dealing with distinct morphological entities. This is perhaps nowhere 

 shown to better advantage than in the aphids, where Stevens (:05, :06, 

 p. 15) has shown that: "In every one of the twenty-four species 

 examined some or all of the chromosomes possess characteristics which 

 distinguish them from their fellows, and these peculiarities persist 

 throughout all the generations. In every species where it has been 

 possible to study and compare the germ cells of the parthenogenetie 

 and sexual generations the single series of the maturating sexual 

 germ cells has been found to be exactly duplicated in the double 

 series of the parthenogenetie egg, the segmenting winter egg and 

 the spermatocytes before reduction." 



The Orthoptera also furnish strong evidence for the individuality 

 of the chromosomes especially in the case of Stenobothrus and Stei- 

 roxys, where, as ])reviously described, the autosomes vary in their 

 method of attachment to the mantle fibers. In Stenobothrus five of 

 the eight autosome pairs always have the mantle fibers attached to 

 one end. In two of the remaining three pairs the mantle fibers are 

 inserted nearer one end than the other, while in the third pair the 

 insertion is at the center. In Steiroxys the insertion is at the end in 

 all except one pair of autosomes, while in that pair it is always near the 

 middle. 



