CHROMOSOMES OF INDIAN RUNNER DUCK. 339 



resemble the pair number 37 in the cells of the male in sutures and 

 constrictions (Fig. 23 a-d), and like them they assume various 

 shapes (Fig. 23, e-i). 



The remaining seventy-two chromosomes in the cells of the 

 female (Nos. 36-1, Figs. 37-42) are approximately the same with 

 respect to behavior, size relations, etc., as those in the cells of 

 the male (Figs. 42-48). 



In my study of the somatic cells I have been increasingly im- 

 pressed with the evident pliancy of the chromosomes. They 

 appear to bend to accommodate themselves to the nuclear wall 

 and to other chromosomal regions. In most of the chromosomes 

 (with certain exceptions to be mentioned later) the degree of 

 pliancy seems to be about equal in all their parts. For this 

 reason the morphology of chromosomes of the same length which 

 are probably synaptic mates is not always the same. The ulti- 

 mate conclusion regarding the shape of each particular chromo- 

 some, I believe, must be drawn from its appearance in metaphase 

 where it is entering the equatorial plate and even in this phase 

 some may be atypical in shape because of the obstructions of 

 other chromosomes. The atypical forms, of course, have been 

 found a lesser number of times and the conclusions are based on 

 the larger number of cases. 



The most convincing evidence is found in a comparative study 

 of the chromosomes when those from different cells are arranged 

 in serial order and in tables as in Plates 7, 8, and 9. Figs. 37 to 

 42 show the chromosomes from cells of the amnion of females; 

 Figs. 43 to 48 from the cells of the amnion of males ; Figs. 49 to 

 54, Plate 9, show first-spermatocyte chromosomes from smear 

 preparations of adult testes. In these tables the constancy of the 

 size and shape of the individual chromosomes stand out at once. 

 There is some variation in form of the chromosomes from cell to 

 cell but it is due, I believe, as previously stated, to their pliancy 

 and in some instances to the particular angle at which the chromo- 

 some lies relative to the observer, and probably more than any- 

 thing else to the particular stage of mitosis in which the cell 

 happens to be found. Figs. 37, 38 and 40 are taken from early 

 prophases (Figs. 8, 9, 10); Figs. 39, 41 and 42 are from prophases 

 of later stage (Figs. 13, 12, 16); Fig. 43 is from a cell in early 



