ASSOCIATION OF CHROMOSOMES IN DIPTERA 247 



two each. The members of these groups, according to his 

 observations are aheady actually associated in symmetrical 

 pairs in the last spermatogonial divisions and later, in the 

 spermatocytes, undergo synapsis and reduction. 



After once discovering pairing in spermatogonia he returned 

 to the subject again in 1908 with additional evidence based 

 on studies of Ascaris, and again in 1910 with more evidence on 

 the Hemiptera. 



In 1902 Sutton described a significant case (Brachystola) 

 in which he believed that all of the chromosomes could be assorted 

 into pairs according to size characteristics. It should be noted 

 that the chromosomes in Brachystola are not actually arranged 

 in pairs, and that the size differences between them are scarcely 

 sufficient to make possible an accurate analysis; yet in spite of 

 this the probabilities afford strong support to Montgomery's 

 deductions. Further support was given by Janssens and Wil- 

 lems ('08), whose description of paired chromosomes in sper- 

 matogonia of Alytes corroborated that of Montgomery on Ple- 

 thodon. Similarly, the studies of Wilson, Payne and others 

 on the Hemiptera, of McClung and his students on Orthoptera, 

 of Stevens on Coleoptera, and of various others, plainly demon- 

 strated that in animals possessing chromosomes of different 

 sizes and shapes there are always two (or multiples of two), of 

 each kind (excepting the sex-chromosomes of the male). 



Contemporaneously with these researches in the field of 

 zoology, there was taking place a strikingly similar development 

 along botanical lines. Indeed it is an interesting coincidence 

 that almost simultaneously with Montgomery's discovery of 

 pairing in the spermatogonia of Syrbula, Strasburger ('05) ob- 

 served a like association in certain plants. He even went one 

 step further than Montgomery in finding the paired association 

 in somatic cells, entirely distinct from the germinal tissues. 

 In embryonic nuclei of Galtonia candicans he found four small 

 and eight large chromosomes, which exhibited an association 

 in pairs. Likewise in Funkia Sieboldiana he observed twelve 

 large and thirty-six small chromosomes showing a similar paired 

 relationship, ''Ich habe zu oft in den Geweben von Galtonia, 



