228 WM. REES B. ROBERTSON 



In the Diptera Stevens ('08) describes V's in nine genera. 

 She has not distinguished, however, between the true V and the 

 ^V-simples' of Gregoire. No points of constriction or segmenta- 

 tion at the apices are in evidence except in Drosophila ampelo- 

 phila (figs. 57-82), in which there are two pairs of V's, a pair of 

 M-chromosomes, and a pair of unequal sex chromosomes. Metz 

 ('14) has found in eight species of the genus unmistakable evi- 

 dence of the compound nature of these V's, since in some species 

 one pair of V's may be replaced by two pairs of rods, and in 

 other species both pairs of V's may be replaced by four pairs of 

 rods. 



Among vertebrates the Dipnoi (Lepidosiren) and the Amphibia 

 afford striking examples of V-shaped chromosomes. In Am- 

 phibia from ten to eleven of the twelve pairs of chromosomes 

 are V-shaped, and only one or two pairs rod-shaped; e.g., Flem- 

 ming ('87, figs. 41, 42, 43a, 44) and Driiner ('94, '95) in Sala- 

 mandra; Eisen ('03), Janssens et Dumez ('03), and Janssens 

 ('05, figs. 69-71) in Batrachoseps ; Carnoy et Lebrun ('99, figs. 

 103, 104, 118) in Triton; Lebrun ('02, figs. 33-35, 41, 42) in oogen- 

 esis of Diemyctilus; Montgomery ('03) in Desmognathus and 

 Plethodon, and Muckermann ('12) in urodeles. 



The arms of the V's in Amphibia are seldom of equal length 

 (Janssens, '02), as is clearly shown by Muckermann in somatic 

 mitoses, where (his figs. 1-4) ten pairs are either V's or J's 

 and only two pairs are rods. Three pairs of the V's have sharp- 

 angled apices, and some appear constricted at this point, as was 

 also shown by Eisen ('00, figs. 112, 120h, 120k). The constric- 

 tion, accompanied by a clear non-staining bridge, was shown 

 by Montgomery ('03) in the chromosomes of the first spermato- 

 cj^te, which were in synapsis. 



That transverse segmentation occurs in Amphibia is clear 

 •from the works of Meves ('07) and Delia Valle ('07), who de- 

 scribe in somatic cells from various tissues of Salamandra chromo- 

 somes thus segmented and showing at the same time the longi- 

 tudinal split. According to these authors, and others who 

 describe similar figures (Bonnevie, '08, '11; Popoff, '08; Haecker, 

 '07), these aj-e examples of hetero typical (tetrad-like) divisions 



