86 E. L. SHAFFER. 



D. OBSERVATIONS. 

 i. Spermatogonia and Diploid Chromosome Groups. 



In all of the species of Lachnosterna studied, as well as Peli- 

 donota and Cotalpa, the diploid number of chromosomes as shown 

 in the spermatogonia is twenty, including an unequal (sex) pair 

 (Figs. 1-6). Dividing follicle cells in the ovaries show ten equal 

 pairs of chromosomes (Fig. 7). There are three pairs of J- or 

 U-shaped chromosomes, one pair of which is considerably larger 

 than the others (Figs. 1-5, A A). The sex chromosomes are the 

 smallest in the complex, consisting of a very small round chro- 

 mosome (;y) and a somewhat larger rod-shaped chromosome (x). 

 In comparing the size relations of the chromosomes in the 

 several species studied, one finds no marked differences. In 

 many cases the chromosomes in the diploid complexes are 

 arranged in pairs, homologous chromosomes lying beside each 

 other. In the Diptera, Metz (1916) has found that pairing of 

 chromosomes is not confined to the maturation stages, but at 

 each cell division homologous chromosomes come together. In 

 the Diptera the diploid chromosome number is relatively low; in 

 species where the. chromosome number is high, pairing of homo- 

 logous chromosomes is usually not found to be so complete. It 

 therefore seems that chromosome pairing, outside of the matur- 

 ation stages, is related to chromosome number. 



In the spermatogonial telophases, the chromosomes spin out 

 into fine chromatic threads (Fig. 13) and as the nucleus grows 

 the threads become more and more complex forming a chromatic 

 reticulum or typical resting nucleus. This "resting" nucleus 

 is of relatively short duration, for soon the chromatin begin to 

 condense into heavier threads (Fig. 15), and as condensation 

 continues, all the chromatin of the nucleus becomes confined into 

 large chromatic blocks of a granular nature (Figs. 16, 17). 

 Counts of these chromatic blocks in uncut nuclei always approxi- 

 mate the diploid chromosome number and these blocks may be 

 considered as the anlages of the future spermatogonial chromo- 

 somes. The blocks consist of a linin-core on which are imbedded 

 the chromatin granules; they are connected to each other by a 

 fine net-work of linin which seems to be continuous with the linin 

 forming the core of the blocks. Most of the cells in the spermato- 



