SPERMATOGENESIS OF APHIDS. 35! 



ess of the formation of the chromosomes is almost finished. 

 There are ten chromosomes, five larger and five smaller, in the 

 equatorial plate of the first spermatocyte division, and they are 

 connected with one another by linin threads as is shown in Figs. 

 4 and 5. The side view of the mitotic figure shows centrosomes 

 of about the same size agreeing with von Baehr's observation on 

 Aphis saliceti (Fig. 3). 



In the anaphase unequal cell division is indicated. The larger 

 and smaller daughter cells are connected by a bridge of cyto- 

 plasm, and elongated lagging chromosomes lie between the chro- 

 mosomes passing to the daughter cells (Fig. 7). The lagging 

 chromosomes do not show any tendency to go to the larger cell 

 at this time, but after the nuclear membrane is formed, the lag- 

 ging chromosomes enter the larger cell (Fig. 8). It is interesting 

 to note that the size of the nuclear membrane -is larger in the 

 larger cell. The inequality of the size of the nuclei of the daugh- 

 ter cells, therefore, does not seem to be due to the unequal num- 

 ber of the chromosomes, but to an unequal quantity of cytoplasm. 

 In a case where the two daughter cells were about equal the size 

 of the nuclear membrane was about the same. 



I have observed many cases in which the lagging chromosomes 

 appear to be divided, but I doubt that this ever occurs. Morgan 

 (1909) states: "That artificial conditions, such as handling or 

 osmosis, might break such a delicate connection at this time is not 

 at all improbable, and such an artificial result might give the im- 

 pression that the accessory is actually divided. Moreover, if the 

 bridge arches toward or away from the observer, the effect may 

 be produced at certain focal levels of discontinuity between the 

 ends of the lagging chromosomes, when none such exist." 



The larger secondary spermatocyte receives eight divided and 

 two lagging undivided chromosomes, and the smaller secondary 

 spermatocyte receives eight divided chromosomes. 



2. Larger Secondary Speniiatocyte. 



The larger secondary spermatocyte undergoes an equal second 

 division without an intervening resting stage. The equatorial 

 plate (Figs. 12 and 13) of the second division shows ten chro- 



