SPERMATOGENESIS OF THE PIG. l"J 



phases of the divisions of spermatocytes of the first order, the 

 daughter chromosomes here retain the rounded appearance and 

 increased size that is characteristic of the bivalent types (com- 

 pare Figs, i, 10, and n, 13, 14, 15, 16 and 17). Thus while half 

 of the spermatids receive five, and half seven chromosomes, in 

 terms of univalence the numbers would in all probability be ten 

 and twelve respectively." 



Jordan ('n) in speaking of the same condition in the opossum 

 remarks as follows: 



"Similarity of form between the chromosomes of the first and 

 second metaphase plates (i. e., double rods) suggests a similar 

 manner of division: accordingly a second reduction. When one 

 recalls, however, that a resting stage (Figs. 39 to 41) usually 

 intervenes between the first and second maturation divisions, 

 when the chromosomes pass through a reticular phase, the above 

 conclusion is inadmissible; or rather, no definite conclusion 

 respecting the character of the second division is justified. A 

 double true reduction, suggested by the form of the chromosomes 

 is contrary to our fundamental conceptions regarding the signifi- 

 cance of chromosomes and need not, in view of the nature of the 

 evidence, be seriously considered. Moreover, in the stage just 

 preceding the brief resting phase of the spermatids (Figs. 57, 58 

 and 59) there occurs a resolution of the five chromosomes into 

 nine and of the four into eight. This demonstrates that the 

 true character of the second division is equational. The second 

 numerical reduction involves a less close union apparently than 

 the first, as a comparison of illustrations 29 and 43 will show. 

 Again the fusion is sometimes incomplete to the extent of giving 

 an occasional count of six chromosomes." 



My own belief that the real character of the second division in 

 the case of the pig is simply equational is based on a number of 

 facts. Even after the first maturation division the ordinary 

 chromosomes are much larger than the spermatogonial univalents. 

 This increase in size has evidently taken place during the growth 

 period of the primary spermatocyte (compare Figs. 1 8 and 38). 

 During the prophase of the secondary spermatocyte the chromo- 

 somes apparently increase still more in size and four large bi- 

 valent autosomes appear for division in the one type of cell and 



