482 Alice M. Boring 



somes end to end is visible soon after they have lost their smooth 

 contours (Fig. 9). 



The last spermatogonial telophase is followed by a dense, darkly- 

 staining contraction stage, which looks like a tightly wound spi- 

 reme. Here the outlines of the chromosomes and their connections 

 are entirely obliterated. The contracted mass occupies only a 

 part of the nucleus, leaving a large clear space at one side (Fig. 10). 

 This space appears in preparations where the fixation of other 

 parts seems to be perfect, so it can hardly be looked upon as an 

 artefact, as McClung ('00) at first claimed. I have used Wilson's 

 ('05b) expression, "contraction stage" as simpler than McClung's 

 "synizesis," for the most condensed period of "synapsis" as 

 Moore used the term. The chromatin now goes through a series 

 of changes comparable to those of Anasa tristis (Wilson '05c) : 

 (i) an early postsynapsis, with a fine spireme, much twisted on 

 itself, still staining deeply, but filling the nucleus much more com- 

 pletely than in the contraction stage (Fig. 11); (2) a late post- 

 synapsis, with the spireme filling the cell completely, less twisted, 

 and staining unevenly (Fig. 12); (3) an early growth stage, with 

 the spireme thicker, the basichromatin aggregated at regular 

 intervals along the linin (Fig. 13); (4) a rest stage, where the spi- 

 reme scarcely stains at all, and in the midst of the pale nucleus (in 

 iron haematoxylin) there is one lens-shaped black body (Fig. 14), 

 which, following Stevens, I shall call the odd chromosome. It is 

 the "accessory of McClung, the "chromatin nucleolus" or hetero- 

 chromosome" of Montgomery, the "chromosome speciale" of 

 de Sinety, or the "heterotropic chromosome" of Wilson. From 

 the action of similar bodies in related species, I am convinced that 

 it must be present here in the postsynapsis and early growth stages, 

 but the spireme stains so deeply and twists on itself so much that 

 it hides the odd chromosome. In the succeeding stage, where the 

 spireme becomes longitudinally split, the odd chromosome length- 

 ens out and loses the smoothness of its outline, although not the 

 intensity of its staining reaction (Fig. 15). The spireme next 

 divides into ten segments, each retaining its longitudinal split 

 (Fig. 16). Counting the odd chromosome, which remains closely 

 applied to the nuclear membrane, there are now 1 1 chromatic 



