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 (Ascaris megalo- 

 ceplmla), X 770. (From photographs.) 



tindle (sp.) t 

 |jng out of 

 ' ig from 



'(chr.) 



A. Lateral view of the egg during the first cleavage; showing the nuclear 



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

 focus, and the asters (as.) formed by fine threads of protoplasm ra " 

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



B. The same stage viewed from one pole, showing the four V-shaped chronics 



in the equatorial plate. 



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



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



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 



