CHROMOMERES 



135 



64, A, D) and between the conjugating chromosomes in the meiotic 

 prophase (Figs. 64, C, and 66) is very striking. The latter phenomenon 

 is speciahy significant, suggesting that syndesis does not concern the 

 chromosomes as wholes, but that it takes place between the separate 

 elements of which they are composed. 



The thesis formulated at the beginning of this chapter requires that 

 the chromosomes should not merely be composed of smaller units, but 

 that these should be differentiated among themselves. It further follows 







Fig. 64. 



Chromomeres. A, epithelial cell of the salamander (Flemming, 1882) ; B, prophase of nucleus in root 

 tip of Najas marina (after Miiller, A.Z., 8, 1912) ; C, zygo-pachytene nucleus of oocyte I. of Enteroxcnos (after 

 Bonnevie, J.Z., 1906) ; D, prophase chromosomes from alimentary canal of Culcx (after Holt, J.M., 1917). 



that if in syndesis corresponding elements of the homologous chromosomes 

 pair together, these elements must always be arranged in the same order 

 along the length of the chromosome. 



Evidence that the longitudinal differentiation of the chromosomes 

 is of a definite and relatively constant nature has been presented in the 

 case of Lepidosiren (Agar, 1913). In this animal the 38 somatic chromo- 

 somes are usually V-shaped, but in the shorter ones the limbs of the 

 V's tend to diverge, till at length the chromosome, by straightening out, 

 becomes rod-shaped. The point of bending of the V can however be 



