STUDIES ON CHROMOSOMES 401 



undergone wide separation. Such, for instance, is the view of 

 BrunelH ('11) in an interesting recent work on Tryxalis; and a 

 similar view is suggested on the botanical side by the recent work 

 of Digby ('10) on Galtonia, and of Eraser and Snell ('11) on Vicia. 

 All these observers believe the longitudinal duality of the spireme 

 threads at the synaptic period to be quite comparable to that of 

 the diploid prophases, and to be traceable to a longitudinal split 

 that is already present in the preceding telophase-chromosomes 

 (cf. also the work of Dehorne and of Schneider, already cited), and 

 these writers emphasize the fact that the products of this fission 

 do in fact separate more or less widely as the nuclei enter the 'rest- 

 ing' period. As to the subsequent changes Brunelli concludes, 

 ''Successivamente, le due meta longitudinale degli individut 

 cromosomici si parallelizzerebbero : donde gli aspetti intermedi 

 che sono stati descritti come scissione di un filo unico, o come 

 I'acollimento di due fill cromatici avendi il valore di due cromo- 

 somi (ipotesi della zigotenia)" ('11, p. 9). It is evident from 

 this how essential it is to determine the number of pre-synaptic 

 threads; for if they have such an origin as has just been indicated, 

 their number should be tetraploid (double the diploid), whereas 

 if they represent whole chromosomes the number should be 

 diploid. 



In the insects that I have studied the pre-synaptic stages are of 

 especial interest as affording almost a demonstration that the pre- 

 synaptic number of threads is the diploid number. I attach 

 great weight to the history of the sex-chromosomes in these stages ; 

 for, owing to the fortunate circumstance that they are individu- 

 ally recognizable at this time, we can be perfectly sure that at 

 least one pair of chromosomes of the diploid groups is here repre- 

 sented by two separate chromosomes that afterwards undergo 

 synapsis. When we consider that these chromosomes are hardly 

 distinguishable from the other chromatic masses of Stage b until 

 after considerable extraction, that the latter are of the same or 

 nearly the same number as that of the spermatogonial autosomes, 

 and that they give rise to the separate leptotene-threads that 

 enter synapsis, we must admit that strong ground is given for 

 the conclusion that the latter are individually representatives of 



