MALE REPRODUCTIVE CELLS 



445 



with pale reticulum and an occasional karyosome. Nothing resem- 

 bling an accessory chromosome or even a plasmosome can be detected. 

 The cells divide mitotically (occasional amitotic divisions also occur) 



FIG. 407.- Male reproductive cells of Aplopus Mayeri. i, resting primary spermatogonium; 

 2, chromosome count of dividing primary spermatogonium; 3, resting secondary spermato- 

 gonium showing accessory chromosome; 4, equatorial view of the 35 chromosomes of sec- 

 ondary spermatogonial division; 5, equatorial view of the 36 chromosomes of a dividing 

 egg-follicle cell of female. X 1400. (Drawn by H. E. JORDAN.) 



in the ordinary homeotypic fashion and the equatorial plate yields a 

 chromosome count of 35 (Fig. 407, 2); none of these can be definitely 

 identified as the future accessory. During the resting stage of the 

 secondary spermatogonial cells (Fig. 407, 3), the accessory chromosome 

 appears as a deep staining body amid the pale reticulum, situated close 

 to the nuclear wall. Sometimes there appears a suggestion of a bipartite 

 structure and occasionally even of a compact skein structure. The cells 

 always divide by homeotypic mitosis, and the equatorial plates again 

 contain 35 enlarged chromosomes (Fig. 407, 4). There are six or 

 seven generations of secondary spermatogonia and only during the 

 telophase of the final spermatogonial division (prophase of primary 

 spermatocytes) does the accessory chromosome retain its compact form 

 and deep staining capacity (Fig. 408, 6) among the ordinary, pale 

 mossy chromosomes, and thus passes over, in original form, into the 



FIG. 408. Aplopus Mayeri. 6, telophase of final spermatogonial division; 7, resting stage of 

 pre-synaptic period ; 8, formation of chromatin lattice and lengthening of accessory chromo- 

 some; 9, spireme loops and accessory chromosome of pre-synaptic growth period; 10, open- 

 ing of chromatin loops before synapsis; n, synapsis of chromosomes. X 1400. (Drawn 

 by H. E. JORDAN.) 



resting or pre-synaptic stage of the growth period of the primary sper- 

 matocyte (Fig. 408, 7). Figure 407, 5, shows a metaphase group of a 

 dividing follicle cell of the ovary with 36 chromosomes. The primary 



