THE VITAL PHENOMENA OF THE CELL 



195 



For examination with reagents, and especially for studying 

 chromatin figures, the eggs of Echinoderms are not so suitable as 

 those of Ascaris. The loop-like nuclear segments are especially 

 small and numerous in them, so that even with the strongest 

 powers they only look like small granules. Fig. 91 represents a 

 spindle, which has been treated with reagents and staining solu- 

 tions ; it corresponds somewhat to Fig. 89, where the living egg 

 is depicted, and may therefore be considered to complete it. 



The process of segmentation may take a fairly long time in very 

 large eggs, such as Frogs' eggs, where a considerable amount of 





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Fig. 91. 



Fig. 92. 



Fig. 91. Nuclear figure of an egg of Strongylocentrotus, one hour and twenty minutes 

 after fertilisation. Reagents have been used. 



Fig. 92. -A portion of the upper hemisphere of an egg of Sana temporaria a quarter 

 of an hour after the appearance of the first furrow, when the coronal radiation is most 

 sharply and plainly defined. (After Max Schultze, PI. I., Fig. 2.) 



yolk has to be divided. Consequently a second process of division 

 may commence before the first is completed. In Frogs' eggs an 

 interesting appearance may be observed, which has been described 

 under the name of the coronal furrow (VI. 68) (Fig. 92). This 

 first furrow commences to appear on a small area of the black 

 pigmented hemisphere of the egg, which is directed upwards ; as 

 it penetrates into the substance, it increases in length, and, during 

 the course of half an hour, extends itself round the whole peri- 

 phery of the globe, appearing last upon the bright surface, which 

 is turned downwards. At this place it penetrates less deeply into 

 the yolk. When it first appears, it is not smooth in appearance, 



