l68 Papers from the Marine Biological Laboratory at Tortugas. 



likewise revealed. The illustrations of the oocytes of the cat by Winiwarter 

 and Sainmont (see figs. 27a, 33, and 44) answer to the main criterion, namely 

 morphological, for the presence of a heterochromosome, "split monosome." 

 A comparison of the illustrations of the spermatocytes and oocytes of the 

 cat as given by Gutherz and by Winiwarter and Sainmont respectively 

 does not seem to warrant the conclusion of an homology between the hypo- 

 thetical X-element in the male and that in female germ-cells of the cat. 

 In short, the oocytes would seem to contain, the spermatocytes to lack, 

 typical X-elements. 



SQUIRREL. 



The spermatogenesis of the squirrel has been described in two papers by 

 Van Molle (1906, 1907). The cells are relatively very large and the idio- 

 some is very distinct. My observations agree with the illustrations of 

 Van Molle with respect to the absence of heterochromosomes. Duesberg 

 (1910) has recently questioned the accuracy of Van Molle's observations 

 with respect to the details of the later stages in the metamorphosis of the 

 spermatid. Interest in these details is outside the scope of this contribution, 

 and my observations on these points have not yet been carried to an extent 

 where I might confidently presume to express an opinion. The absence of 

 any accessory chromosomal element during the growth period appears un- 

 questionable. 



PIG. 



It will suffice for present purposes to state simply that evidence of an 

 accessory or heterotropic chromosome at early stages of the spermatogenesis 

 of the pig is completely lacking in my material. The cells here are relatively 

 small; but the fixation is good and reveals clearly all the details of structure, 

 and every phase is abundantly represented prior to the division phases ; oc- 

 casionally first maturation groups are also present.^ 



RABBIT. 



Exactly the same statement holds for the rabbit as for the pig; and I 

 make it with greater confidence, since the material is more extensive 

 including besides adult testes those of new-born and young individuals. 



In all of the foregoing instances the spermatogonia contain plasmosomes. 

 The resting primary spermatocytes also contain either plasmosomes or 

 karyosomes (net-knots), or both, all of which disappear in early presynapsis. 

 It seems legitimate to assume, on the basis mainly of this observation, that 

 in mammals generally plasmosomes almost invariably disappear before 



1 However, no chromosome counts were attempted. In view of J. E. Wodsedalek's recent work ("Acces- 

 sory Chromosomes in Pig;" Science, N. S., vol. xxxviii. No. 966, pp. 30-31) reporting two additional chro- 

 mosomes or accessories in half of the secondary spermatocytes — this number (10) corresponding with the re- 

 duced number in the eggs — the pig can no longer be listed under "exceptions." In the absence of definite 

 evidence during the growth period, the final criterion for the presence of heterochromosomes must be an actual 

 count. 



Since the appearance of Wodsedalek's complete paper (Biol. Bull., 25: i), I have carefully re-examined 

 my sections of the pigs' testes. Mitoses are too infrequent to warrant any statement concerning the presence 

 or absence of accessory chromosomes on the basis of appearances at metaphase, or of chromosome counts. 

 My conclusions rested upon evidence drawn from a study of appearances during the growth stages including 

 the early prophase. As to the resting spermatogonial and primary spermatocyte nuclei I find no such con- 

 stancy with reference to nucleoli as Wodsedalek records. The number, both of the large and smaller nuc- 

 leoli, is very variable. Three or four large nucleoli are common. Moreover, with reference to the chro- 

 mosome-nucleoli I can not find in my preparations (of young testes) any cells to parallel his illustrations 21, 23, 

 24, and 25. My material does not confirm his finding that "two large round nucleoli remain very conspicuous 

 throughout the process of growth of the primary spermatocyte." 



