70 



GENERAL PHYSIOLOGY 



centrosome in the form of a radiating aster ; the centrosome forms 

 the middle point of the star-shaped figure (Fig. 10), and is easily 

 discovered by this peculiar investment. . 



While many investigators, led by van Beneden, are inclined 

 to regard the centrosome as a specific constituent of the cell, since 

 it is always to be found in the protoplasm apart from the nucleus, 

 O. Hertwig ('92) upholds the view that it belongs to the nucleus 

 as a part of the nuclear substance, and passes from it into the 

 protoplasm only during the activity of the former in fertilisation 



Oboo* 



Fio. 11. — Division and withdrawal of the centrosome in the nucleus of the spermatozoa of 

 Ascaris megalocephala ; the twoupper rows show successive stages of the nucleus (w . nucleolus ; 

 f, centrosome) ; below, two spermatozoa after the wuthdi-awal of the centi'osome from the 

 nucleus. (After Brauer.) 



and division, retreating afterwards again to the nucleus as a part 

 of the substance of the latter during the resting-condition of the 

 cell. That this view of Hertwig is applicable in certain cases has 

 been shown recently by the striking investigations of Brauer 

 ('93, 2) upon the development of the spermatozoa of the thread- 

 worm, Ascaris vicgalocephala. Brauer was able to determine that 

 in these cells the centrosome is contained within the resting 

 nucleus, and in certain cases even undergoes division there ; later 

 it wanders out into the protoplasm and there produces the proto- 

 plasmic radiation which surrounds it during cell-division (Fig. 11). 



