714 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of cytoplasm. The autosomes of the spermatogonia vary greatly in size, 

 and can be readily arranged in symmetrical pairs, which usually lie 

 close together, and show constant and characteristic differences in both 

 form and size. A monosome is always present. The oogonia contain 

 one more chromosome than the spermatogonia, there being a symmetrical 

 pair in place of the monosome. In the resting spermatogonia of 

 Steiroxys trilineata the monosome is enclosed within a separate vesicle. 

 During the telophase of the last spermatogonial division, the monosome, 

 which is enclosed within a distinct vesicle, retains its compact form, and 

 often shows a more or less distinct bipartite structure. The first stage 

 of the primary spermatocyte is characterised by the chromatin being 

 evenly distributed through the nucleus in a finely granular condition. 

 Later, the chromatin collects in more or less definite masses, which in 

 favourable cases (Chortophaga, Melanoplus) can be seen to be of approxi- 

 mately the same number as the autosomes of the spermatogonia. Each 

 chromatic mass later becomes converted into a single spireme thread, 

 composed of a single series of chromatin granules connected by linin. 

 The spireme threads become converted into loops having a polar arrange- 

 ment, each loop being composed of two homologous autosomes joined 

 end to end. The polar loops later show a more or less distinct longi- 

 tudinal split. This split, however, does not extend to the linin, but is 

 produced by each chromatin granule dividing into two equal parts. 

 Later the longitudinal split becomes temporarily indistinct, and may 

 entirely disappear, while the loops open out and assume a peripheral 

 position. In the early growth-period the monosome becomes enclosed 

 within the nucleus, where it forms a somewhat flattened, deeply staining, 

 often vacuolated element, closely applied to the nuclear membrane. 

 During the later growth-period the monosome goes through a com- 

 plicated development, which is to a certain extent comparable to that 

 undergone by the autosomes during the same period. In Stenobothrus 

 and Melanoplus the monosome divides into two dissimilar parts, which 

 can be distinguished up to a late stage in the prophase of the first 

 maturation division. Each polar loop of the growth-period develops 

 into a definite tetrad during the prophase of the first division. The 

 bivalent autosomes or tetrads show the same size relations as the auto- 

 some pairs of the spermatogonia, and are evidently formed by the con- 

 jugation of the components of each pair. In addition to the difference 

 in volume the bivalent autosomes show constant and characteristic 

 differences in form. In general, several more or less distinct morpho- 

 logical types can be distinguished, and the members of each type appear 

 to bear a constant numerical relationship to each other. 



The first maturation division is reductional, separating chromosomes 

 which united during synapsis. The second division is equational. 

 Individual chromosomes differ in regard to the point of insertion of the 

 spindle fibres during mitosis, but for each chromosome this point is 

 constant throughout the spermatogonial and spermatocyte divisions. 

 The monosome does not divide in the first division, but divides longi- 

 tudinally, and probably equationally in the second. The spermatids 

 are dimorphic, one half containing a monosome, while the other half 

 lack this element. The monosome remains compact for some time 



