THE VITAL PHENOMENA OF THE CELL 



189 



visible on the surface of the cell-body, corresponding to a plane, 

 which passes perpendicularly through the centre of the nuclear 

 axis, uniting the two centrosomes ; this has already been 

 referred to as the plane of division. " The furrow commences on 

 one side, and gradually extends itself round the equator; how- 

 ever, it remains somewhat deeper on the side where it commenced 

 than on the opposite one " (Flemming). This ring-like constric- 

 tion gradually cuts more and more deeply into the cell body, until 

 finally it divides it completely into two nearly equal parts, each 

 of which contains a daughter nucleus, undergoing the process of 

 reconstruction. As soon as division is complete, the polar radia- 

 tions commence to fade away. 



The above-mentioned connecting fibrils between the daughter 

 nuclei may be distinguished, in many objects, until division is 

 completed. They are then severed in their centres by the cutting- 

 through of the cell-body. Sometimes a number of spherical 

 swellings, which become intensely stained, may be seen at this 

 time to develop at the centres of the spindle fibrils ; these Flem- 

 ming (VI. 13 7/ ) has named separation bodies, and he considers 

 that they probably represent the equatorial plates of plants, 

 which are much better developed. 



b. Division of the egg-cells of A scan's megalocephala and 



Toxopneustes liuidus. The nuclei of the eggs of Ascaris are re- 

 markable for the size and distinctness of their centrosomes, and 



for the small number of their nuclear segments, of which in one 



species only four, and in another only two, are present. Another 



very important phenomenon, the multi- 

 plication of the centrosomes by division, 



may be especially clearly seen in this 



object. It is best to commence our in- 

 vestigations at that point when the egg 



has just developed the furrow, and when 



the four nuclear loops on either side of 



the plane of division have transformed 



themselves into a vesicular nucleus of 



irregular outline (Fig. 82). The side of 



the nucleus, which is directed towards 



the pole, has several ragged processes, 



the nuclein being spread out upon its 



loose network. The centrosome may still 



be distinguished in the neighbourhood of 





Fig. 82. Egg of Ascaris 

 megalocephala undergoing the 

 process of double division. 

 Nuclei are resting ; the cen- 

 trosomes as yet undivided. 

 (After Boveri, PI. IV., Fig. 74.) 



