j;02 Alice M. Boring 



THEORETICAL CONSIDERATIONS 



Individuality of the Chromosomes 



The theory of the individuahty of the chromosomes was first 

 proposed by Boveri ('88) as a result of his work on Ascaris. He 

 found a constant number of chromosomes in each species, always 

 half this number in the two maturation divisions, and the original 

 number restored by fertilization. Every year adds to the number 

 of species found conforming to these rules, and consequently 

 making Boveri's theory more plausible. Beginning with Sutton's 

 work in 1900, many species have been shown to give evidence of 

 a more direct nature, and among these, the Hemiptera Homop- 

 tera can be classed. In the first place, it is a sign of individuality, 

 when we are able to pick out one chromosome in every equatorial 

 plate by some characteristic size, shape or position. This can be 

 done for 14 out of the 22 species of Hemiptera Homoptera 

 studied, the characteristic usually being the large size of the 

 chromosome (see Poeciloptera septentrionalis, Figs. 270, 273, 

 274). Secondly, all evidence that supports Montgomery's hy- 

 pothesis of the union of paternal and maternal chromosomes in 

 synapsis necessarily supports the theory of the individuality of the 

 chromosomes. In Poeciloptera septentrionalis, the large chromo- 

 some in the spermatocytes (Fig. 270) is represented in the sperma- 

 togonia (Fig. 259) by two large chromosomes. Half of the chro- 

 mosomes in each spermatogonial plate must have come originally 

 from the spermatozoon, and half from the egg. Only one large 

 chromosome could be received from the spermatozoon, according 

 to Fig. 270, therefore the other large one must have come from 

 the egg. As these two large chromosomes, one paternal and one 

 maternal, are represented by a single chromatic element in the 

 spermatocyte, this must be formed by the union of a paternal with 

 a maternal chromosome of the spermatogonium. Thus we see 

 that the Hemiptera Homoptera are in accord with Montgomery's 

 hypothesis of synapsis and reduction. In the third place, the 

 behavior of the odd chromosome supports Boveri's theory. In the 

 Hemiptera Homoptera, the odd chromosome can seldom be identi- 

 fied in the spermatogonia, but from the contraction stage to the 



