418 Sidney I. Kornhauser 



VII. The Spermatocyte Divisions. 



In contrast to tlie primaiy oöcyte metaphase (Fig. 49, Plate VI) 

 in Avhich the chromosomes are easily counted, tlie metaphase plates of 

 the primary spermatocytes present great difficulties. This is understood 

 when one views the spindle lateraUy (Fig. 29, Plate VI). Here the 

 chromosomes are of such a varied form — long rod-like forms with 

 thickened ends, ring forms as in the oöcyte, and single rods lying with 

 their long axes in the equator — that it is almost impossible to make 

 an accurate count of the number, unless the plate is viewed exactly 

 f rom one of the poles of the spindle. Twenty-three such plates were dr&vm : 

 in seventeen cases thirteen chromosomes were present (Fig. 27, Plate V), 

 and in six cases twelve chromosomes (Fig. 28, Plate V) were counted. 

 As later stages show, this Variation is due to the conjugation or lack of 

 conjugation (in about three-fourths of the cases) of a pair of chromo- 

 somes (h, h, Figs. 29—32), which lag behind in the anaphase. AVhethcr 

 this pair of chromosomes is exactly comparable to tHe paired "sex-chro- 

 mosomes" is an open question; but, in their behavior during the matura- 

 tion divisions, they do resemble the hetero-chromosomes of RhaMitis 

 (BovERi, '11; Schleif '11), and certain Coleoptera and Diptera described 

 by Stevens ('08; '09). In Rhabditis there are six tetrads in the primary 

 oöcyte, whereas in the primary spermatocyte metaphase there are seven 

 chi'omosomes, — five tetrads, and two diads, the hetero-chromosomes. 

 Schleif found also that the hetero-chromosomes were occasionally joined 

 to one another, so that six tetrads, as in the oöcyte metaphase, could be 

 counted. These hetero-chromosomes in RhaMitis are evident in the 

 growth period where they are more compact than the autosomes and 

 in contact with the nucleolus. In Hersilia a search for the hetero-chro- 

 mosomes in the growth period was unavailing; the only indication of 

 anything unusual in the chromatin bands was the precocial Separation 

 of a pair of conjugants before the end of the bouquet stage, and this was 

 found in only three cases. 



Figure 30 represents an early anaphase. The autosomes separate 

 reductionaUy, whole chromosomes transversely marked by a "Querkerbe" 

 passing to the poles. The hetero-chromosomes {h, li), each attached 

 to both groups of separating autosomes, lag behind. A stage some- 

 what later, which is even more striking, is shown in Figure 31. Cells 

 in this condition are not at aU uncommon, in fact they are far more 

 plentiful than metaphase or telophase figures, indicating that the lagging 

 of the hetero-chromosomes is a phenomenon of considerable duration. 

 Owing to the Variation in form, it was not possible to establish a morpho- 



