66 H. B. GOODRICH 



ing transversely across the parallel threads of the stage of figure 

 12, but as the relation of these structures to those of the diplo- 

 tene stage is uncertain, it cannot be assumed that a transverse 

 division of the double prophase threads would be equivalent 

 to a similar division of the quadripartite threads of the pre- 

 ceding stage. After fixation with Hermann's fluid the tetrad 

 structure is not visible in the late prophases (fig. 36). The nu- 

 clei show thirteen bivalent, six univalents (seven if the micro- 

 some can be identified) and one tripartite group; these repre- 

 senting respectively the thirteen autosome bivalents, seven of 

 the X-elements and the long X-component associated with its 

 mate the Y chromosome. The plasmasome may also be dis- 

 tinguished. The tripartite group is of too regular occurrence 

 to be confused with an approximation of a univalent and a 

 bivalent chromosome and as indicated above the enumeration 

 of the chromosomes will account for all the autosomes and for 

 seven of the X-components; the tripartite group which remains 

 is similar to the long X-component and its mate the Y-chromo- 

 some as described below when it appears in the maturation divi- 

 sions (page 67). Material fixed in Gilson-Carnoy's fluid and con- 

 siderably extracted clearly shows the compound nature of this 

 typical group (fig. 16). Figure 44 shows the. same group from 

 various nuclei, — c, d, e after Gilson-Carnoy's fixative show 

 clearly its nature, in (c) and (d) there appear three segments, 

 in (e) four and in figure 16 five. The Y is usually identifiable 

 as the larger and more compact terminal segment because the 

 segment at one end is too small to represent a single chromosome 

 and also the widening of the longitudinal cleft at this end is 

 characteristic of the unapposed end of the long X-component. 

 Figure 44, a and b are after use of Hermann's fluid, b from the 

 prophase and a as it lies in the metaphase plate showing an 

 attachment of spindle fibers in harmony with the assumption 

 of its true tripartite nature (see page 66). 



'5. The maturation divisions. Figure 17 shows a polar view 

 of a metaphase plate of the first maturation division. The 

 characteristic X group consisting of eight chromosomes, one the 

 microsome and one longer chromosome, is centrally located and 

 surrounded by a group of thirteen autosomes and the Y-chromo- 



