516 Theophilus s. Painter, 



chromosomes have a distinct longitudinal split as they lie scattered 

 through the nuclear cavity and this split persists until the raeta- 

 phase of the division (Fig. A). After the nuclear wall is dissolved 

 the chromosomes are drawn into the spindle. Neither at this time 

 nor at any later period, has it been possible to pair off the spermato- 

 gonia! chromosomes as Wilson (1906) has done for Anasa tristis, 

 and other Hemiptera, 



Seen from the side the spermatogonial spindle is quite charac- 

 teristic. The centrosomes appear as points and the spindle fibers, 

 arising from them, show considerable bulging, doubtless due to the 

 large number of chromosomes in the cell. A polar view of the 

 equatorial plate (Figs. 3, 4) shows the autosomes closely crowded 

 together and over-lapping to a considerable extent. It has not been 

 possible, for this reason, to make out the exact number of chromo- 

 somes present in the cells, but in one case twenty-eight chromosomes 

 could be easily counted (Fig. 3). This is probably not the full number 

 of spermatogonial chromosomes. 



Accessory chromosomes and ctetosomes. ^) 



Prophase. Up to the time when the autosomes are drawn 

 into the spindle of the last spermatogonial division, no trace of the 

 accessory chromosomes or of the ctetosomes has been found. But when 

 the spindle is fully formed, a large double chromosome is seen lying 

 just outside of the general circle of autosomes. This double body 

 is the accessory chromosome (Fig. 4 A). Lying near the accessory 

 chromosome, shown in Fig. 4, we find two very small bodies marked 

 "C". One of these is larger than the other and during the ensuing 

 divisions they behave as ctetosomes. 



The position of the ctetosomes is extremely variable although 

 the position of the accessory chromosomes is typically shown in 

 Fig. 4. Only in one cell have the two ctetosomes been seen 

 together in this view of the spindle; they are usually hidden by 

 the over-lapi)ing autosomes. 



Metaphase. The metaphase is initiated by the precocious 

 division of the accessory chromosome elements. The two chromosomes 



1) The term "Ctetosorae" (which is derived from the Greek KtrjTog 

 implying that an o})ject belongs to, or is the pro})erty of something) was 

 adopted for these peculiar chromosomes which are always associated with 

 the accessory chromosomes during the first maturation division. 



