STUDIES ON CHROMOSOMES 403 



sens's somewhat similar account of the pre-synaptic stages in Tri- 

 ton have already been mentioned (p. 368). In Batracoseps, on 

 the other hand, there is as -yet nothing to show that the lepto- 

 tene-threads arise directly from the irregular and variable chro- 

 matin-masses that are seen in the earlier stages ('protobroch' 

 and 'deutobroch' nuclei). 



Opinion still differs so widely in respect to the pre-synaptic 

 conditions in plants that its discussion can hardly be under- 

 taken here. Overton ('05, '09) and those who have adopted the 

 'prochromosome-theory' find the leptotene stage preceded by 

 one in which massive 'prochromosomes' are present, of the dip- 

 loid number, and already showing an association in pairs which is 

 a forerunner of actual synapsis; but other observers have found 

 no support for this view in the objects they have examined (cf. 

 Mottier, '07, '09). It seems possible that different species may 

 differ in this respect, as is certainly the case in animals. 



It is impossible to leave this discussion without mention of two 

 additional series of facts which lend strong indirect support to 

 the theory of synapsis. One is the remarkable discovery that in 

 the diploid groups the chromosomes are often found to corre- 

 spond two by two in respect to size, as was first pointed out by 

 Montgomery ('01) and Sutton ('02); and that in some cases the 

 chromosomes are actually arranged in pairs according to their 

 size. The latter fact was also first described, I believe, by Mont- 

 gomery ('04) in Plethodon, later in a number of the Hemiptera 

 ('06) ; and in the latter work first appears the view that such an 

 actual arrangement in pairs is characteristic of the diploid nuclei 

 (p. 148). A similar arrangement was later described by Janssens 

 and Willems ('08) in Alytes; and a most striking, unmistakable 

 case of the same kind was found by Stevens ('08) in several of the 

 Diptera. On the botanical side similar facts have been de- 

 scribed by Strasburger ('05), Geerts ('07), Sykes ('09), Miiller 

 ('09), Gates ('09), Stomps ('11) and others. Overton, Rosenberg, 

 Lundegard, and others likewise describe the ''prochromosomes" 

 as arranged in pairs in the diploid nuclei, as well as in the pre- 

 synaptic stages of the auxocytes. So many of these cases have 

 been described, some of them of quite demonstrative character 



