-I I.KMATOGENESIS OF THE MYRIOI'O 151 



four of the rod --haped chromosomes exclusive of the accessory, 

 which, of cour-e. i- present in but one of the chromosome groups. 

 The chromo-oine groups, as seen in the metaphase of the two 

 cell- derived from one primary spermatocyte are shown in Plate 

 II., I ; L-. MI, 20. The most striking fact to be observed is the 

 absence of ih- -ory chromosome in one of the cells. Kvena 



MI per t"n ial examination, however, shows that in shape and relation 

 to the inaiitli- titters the chromosomes are of several different. 

 t\pe-, am! that these characteristics coincide with what would 

 '1 fmm a study of their earlier history. The chromo- 

 somes deri\ed fn-m the cross-shaped tetrads have altered their 

 -hape i on-.ider.ibly since last seen in the anaphase ol the ln>t 

 maturation <li\i-ioii. They are much shorter and thicker ami 

 are m>\\ l>ilo|..-d bodies the constriction between the lobes repre- 

 senting the plain- of transverse cleavage. The attachment ol 

 ill. mantle liber-; seems to be at no particular point but may be 

 ai an\ pan of each Unite ned end of the dyad. 



Tin- -inn itiral peculiarities of the chromosomes derived from 

 the double Y--haped tetrads are much more characteristic. In 

 -hap.- tin- d\ad- of this type resemble those just described to 

 Mime .Atl-iit. but, except in si/e, bear a more striking resemblance 

 i,, iln double- Y-shaped chromosomes from which they are de- 

 rived. < >n.- end. usually the one nearest the center of the equa- 

 torial plate, is broader than the other, and the entire structure 

 \ei\ , -\idenil\ correspond-, to the single-V-shaped chromosomes 

 ol the iir-t spermatocyte anaphase. The mantle fibers are always 

 attached to the broader end of the dyad, this fact being even 

 more characteristic than the shape. The appearance of these 

 chromosomes \\hilt- in the act of division might lead one to believe 

 that the it Milling division is a longitudinal one, but such a con- 

 clusion \\ould ignore entirely the previous history of this type o| 

 chromo-, .me- during the prophase and metaphase of the fn-t 

 maturation di\ i-ion. 



Chromosomes 1.. M. O and P. in the second spermutocyte 

 (Kiu-. to. jo are the product of the longitudinal division o! the 

 rod--haped tetrads. They are dumbbell-shaped d\ad> with a 

 manile liber attached to each end. The constriction at the 

 mid. lie of each represents the plane of tran>\ er-e division. Chro- 



