SOMATIC CHAKACTERS AND CHR03IATIN liOD-LENGTHS. Ill 



tetrads and the odd chromosome, and in the hitter the odd chromosome is seen 



passing entire to one pole, while the ordinary 

 chromosomes are preparing for or actually 

 undergoing fissionan the equatorial plane. 



The second maturation division immediately 

 follows the first, and the complex is composed 

 of eioht or nine chromosomes, the difference 

 depending upon the odd chromosome, which 

 is found in only 50 per cent, of these cells. 

 As in the case ol: the spermatogonial meta- 

 phases, each ordinary chromosome is composed 



^. ^ ^ ^"'T' X .• of two equal rods, and the same size-relation- 



Fig'. 5. — Second maturation ^ ^. ^ . i 



laitosis. s^ips 'ii"e ^^gain apparent. Fig. o is an example 



of this metaphase seen from the polar aspect. 

 The transformation from spermatids to unripe and ripe spermatozoa is 

 similar to that already described for these organisms by myself and other 

 writers. The chromosomes become dissociated into minute granules, which 

 at first stain only slightly with the iron hsematoxylin ; the appearance of the 

 " centrosome " is accompanied by elongation of nucleus and cytoplasm, the 

 latter eventually constituting a long thread-like tail. ^ 



Dimensions of the Chrobiosomes. 



The diameter of all component rods of the ordinary spermatogonia! 

 ■chromosomes is -83 fi, and these consequently diff'er from one another only in 

 length. The complex is divisible into two groups represented respectively 

 by three long and five short pairs : this grouping accords with that of Davis, 

 and with my own upon other members of the genus. Moreover, the lengths 

 -of the component rods of the five short pairs are respectively I'T, 2-1, 2'5, 

 2-9, and 3-3 yu,, and therefore constitute consecutive members of a series m 

 arithmetical progression ; those of the three long pairs also belong to this 

 series, but are alternate instead of consecutive, being respectively 5-0, 5-8, 

 and 6'7 /i. 



The tetrads or primary spermatocyte chromosomes cannot be measured 

 accurately for their outlines are irregular, but a careful study of the filaments 

 •condensing during the preceding prophase leaves little doubt that they are 

 individually composed of rods of the above dimensions. 



The secondary spermatocyte complex is the most favourable for the 

 measurement of chromosomes, since overlapping does not occur and in- 

 dividuals are composed of pairs of rods as in the spermatogonial mitoses. 

 The diameter of the component rods of ordinary chromosomes is again "83 /i, 

 and the lengths are respectively 1-7, 2-1, 2*5, 2-9, 3-3, 5*0, 5-8, and 6-7 /m, 

 i. e., identical with those of the spermatogonia. The odd chromosome, found 



