CHROMATIN DEVELOPMENT AND HEREDITY 237 



There is no indication that the formative processes that usually 

 accompany cleavage have operated here. Figure 27 is from a 

 section through a Ctenolabrus embryo of the pure breed, which 

 was fixed thirteen hours and forty minutes after fertilization. 

 Although this embryo is younger than that shown in figure 26, 

 the cells show the characteristic arrangement which precedes 

 gastrulation. A comparison of the nuclei of these stages will 

 be made later. 



All of the material of the first cleavage stages obtained was 

 preserved in Perenyi's fluid and not enough of it was examined 

 to warrant any positive statements concerning the mitotic be- 

 havior. Well-fixed material of second cleavage stages are, how- 

 ever, fairly abundant and large numbers of eggs were studied. 



Figure 28 shows a second cleavage metaphase spindle in three 

 sections. The chromosomes are clearly recognizable as elongated 

 rods of various lengths, some of them already attached at one end 

 to fibers at the equator of the spindle. This stage is comparable 

 to that of figures 16 and 17 of Moenkhaus's paper in which he 

 states that division has already begun. The extension, however, 

 of the ends of the longer rods toward the poles in his figures, as 

 in this, does not indicate division, for, as figure 28 shows, the 

 spindle fibers are attached at the end of the rod lying nearest the 

 equator of the spindle or the proximal end, while the distal ends 

 which have not yet been drawn into the equatorial plane and 

 which sometimes project toward the poles are free from spindle 

 fiber attachments. 



Figures 29 and 30 are typical views of second cleavage ana- 

 phases. The longest rods can be identified with certainty as 

 Fundulus chromosomes. They show no abnormality of form or 

 behavior. In favorable sections of early anaphases the separate 

 halves of the chromosomes appear paired, and it is very evident 

 that normal division of the metaphase rods has occurred. The 

 separating ranks are fairly straight. 



Figures 32 and 33 show typical anaphases of the fourth cleav- 

 age. They resemble in their details the earlier cleavage figures. 

 There is no perceptible diminution in size of the Fundulus chro- 

 mosomes at the fourth cleavage stage. The proportionate sizes 



