94 E. L. SHAFFER. 



and maintains the organization of the nuclear elements. Wenrich 

 ('16) has shown how remarkably constant the organization and 

 "architecture" of the chromosomes are. By means of certain 

 structural peculiarities which his "selected" chromosomes 

 presented, he was able to recognize and trace them through all 

 the stages of spermatogenesis. The tendency has been noted 

 in many forms for the chromosomes to appear in the metaphase 

 always in a definite configuration. It is possible that the linin 

 connections between the chromosomes which have often been 

 figured (Figs. 8-12) are responsible for the definite patterns as- 

 sumed by the chromosomes in the metaphase plate. The 

 uniting in pairs of the homologous leptotene threads may be due 

 to the contractility of the linin connectives running between 

 the homologous chromomeres. In short, the morphological 

 stability of the nuclear elements and the constancy of their 

 form, arrangement and organization is in the last analysis 

 referable to the linin. 



F. SUMMARY. 



1. The diploid chromosome groups of four species of Lach- 

 nosterna, namely delala, fusca, gracilis and tristis, as well as 

 Pelidonota punctata and Cotalpa lanigera, show twenty chromo- 

 somes, one pair of which is composed of two unequal elements 

 (sex chromosomes) . 



2. There are no essential differences in the form and arrange- 

 ment of the chromosomes in the species studied. 



3. The growth period of the spermatocytes is marked by the 

 appearance of delicate leptotene threads which are derived from 

 the chromosomes of the last spermatogonial division. These 

 threads become polarized and there is evidence that they are 

 arranged in pairs parasynaptically. 



4. There is a definite contraction stage which does not seem 

 to be caused by fixation, but is a normally occurring phase in 

 the growth period. 



5. The sex chromosomes persist through the entire growth- 

 period in the form of definite compact bodies, sometimes being 

 contained within chromosomal vesicles. The unequal sex 

 elements separate in the first maturation division and divide 

 equationally in the second maturation division. 



