320 N. M. Stevens. 



finds no such intermediate stages as would necessarily appear if 

 this secondary yolk were formed w^ithin the egg as described by 

 Balbiani {'Gg-'yi). The outlines of the yolk cells are lost and 

 only fragments of nuclei are found (Fig. 22), while in Aleurodes 

 several whole yolk cells with nuclei intact enter the oviduct below 

 the egg and are later included in the posterior end of the egg. 



The chromatin in the egg during its growth period offers no 

 favorable conditions for study. In earlier stages it does not take 

 chromatin stains, and in later stages the chromosomes are spheri- 

 cal and mingled with nucleoli ot similar form and staining qualities. 



2. Maturation. 



The earliest stage found in the laid egg w^as that shown in 

 Fig. 23 — the equatorial plate of the first polar spindle, showing 

 5 chromosomes, the reduced number, of the same relative form 

 and size as the chromosomes of the 5 pairs in Figs. 7 and 12. 

 The manner in which the egg chromosomes are paired is not 

 evident, but the two divisions appear to be longitudinal and iden- 

 tical w4th the maturation divisions of the spermatocyte where it is 

 quite certain that they are paired longitudinally, and probable 

 that the first division separates the paired chromosomes. 



Fig. 24 shows the first maturation spindle in metaphase. One 

 chromosome appears in both figures (stippled in b). In Fig. 25 

 the first polar body and the second polar spindle in metaphase are 

 figured. A part of a chromosome appears in a and parts of two 

 in the spindle of b. In Fig. 26, a later stage is seen; the chromo- 

 somes of the first polar body are massed together, those of the 

 second (not yet separated from the egg) show the comparative size 

 relation of Fig. 23, their position indicating a longitudinal division; 

 the chromatin of the egg nucleus is becoming diffuse and less 

 stainable. 



The spermatozoon enters at any point, more often near the pos- 

 terior end of the egg, and leaves a train of cytoplasm behind it, 

 as it traverses the yolk preceded by an aster. Fig. 27 shows the 

 male and female pronuclei, the former distinguished by the cyto- 

 plasmic path (indicated by arrows). I have never found the first 

 segmentation spindle in my material nor indeed the divisions 

 immediately following, though the resting nuclei of these stages 

 have frequently been observed. In the later segmentation stages 



