78 OUTLINES OF EVOLUTIONARY BIOLOGY 



stage, with the chromatin granules collected together in a long 

 spirally coiled thread and the nucleolus still very conspicuous. 

 C shows the group of chromosomes formed by transverse breaking 





FIG. 35. Mitosis in the segmenting Egg of the Horse-Worm (Ascaria mfyolo- 

 cephala), X 770. (From photographs.) 



A. Lateral view of the egg during the first cleavage; showing the nuclear spindle (sp.), 



the equatorial plate (aeq.), one of the two centrosomes (c.s.), the other being out of 

 focus, and the asters (as.) formed by fine threads of protoplasm radiating from 

 around the centrosomes. Polar bodies (p.b.) are also shown. 



B. The same stage viewed from one pole, showing the four V-shaped chromosomes (chr.) 



in the equatorial plate. 



C. The first division is completed and the nuclei have again passed into the spireme stage. 



A polar body (p.b.) is still visible. 



D. Each of the first two blastomeres has again reached the stage represented in A 



and B. 



up of the spireme thread. The karyosome has now disappeared, 

 having apparently been used up in the formation of the chromo- 

 somes. D shows the two groups of daughter chromosomes 

 formed by longitudinal splitting of the parent chromosomes and 

 retreating towards the two ends of the spindle, which is only 



