V . CONTINUITY OF THE CHROMOSOMES 129 



type D produce the nuclei shown in E, which have two equal projections, 

 each containing two chromosome ends. In the next prophases (C, F) 

 the chromosomes reappear in the same arrangement as they exhibited 

 in the previous telophases. It will be noticed that the orientation of the 

 nuclei towards each other in the two daughter cells has changed slightly 

 owing to the rotation of the nuclei within the cells. This however does 

 not affect their internal architecture. 



It must be understood that what we have here described as a process 

 is, Uke all similar work in cytology, really pieced together from a series 

 of fixed stages. Thus it cannot actually be observed that the prophase 

 nuclei of types C and F are the outcome of telophase nuclei of types A 

 and D respectively, but this can be inferred without reasonable doubt 

 since (i) they are connected up by a close series of intermediate stages 

 of which B and E are examples ; and (2) in the prophase, as in the 



/ 



'dm 



\ 



A B 



Fig. 59. 



Showing similar orientation of telophase (A) and prophase (B) in the epidermis of the salamander. 



(Rabl, M.J., 1885.) 



telophase, the arrangement of the chromosomes in the two sister nuclei 

 derived from the previous mitosis is the same. 



An orientation of the chromosomes in telophase similar to that in the 

 succeeding prophase has been described by many cytologists from Rabl 

 (1885) onwards (Fig. 59), though the conditions are seldom so favourable 

 for observation as in Ascaris megalocephala. 



Another fact directly supporting the hypothesis of the genetic 

 continuity of the chromosomes is that each chromosome may undergo 

 its telophase metamorphosis in a more or less separate vesicle within 

 the nucleus. This is especially characteristic of Orthopteran spermato- 

 genesis (Fig. 60). Sutton (1903) described the larger chromosomes of 

 the spermatogonial telophase of Brachystola magna as forming each its 

 own reticulum in a separate vesicle, which however is in communication 

 with the other vesicles at their polar ends, forming there a common 

 compartment from which the vesicles project like the fingers of a glove. 

 This general account has been confirmed by several cytologists. In 

 Phrynotettix (Wenrich, 1916) the telophase chromosomes first form closed 



K 



