THE VITAL PHENOMENA OF THE CELL 



191 



independent individuality. The angles of the loop are turned 

 towards the original pole (the polar area in the Salamandra), 

 whilst the ends of the loop, which are knob-like and swollen, are 

 directed towards the region of the anti-pole. 



The second stage of division now commences. The centro- 

 somes, with their spheres, separate and travel for some distance, 

 until their common axis lies either somewhat obliquely or parallel 

 to the first division plane. The nuclear membrane dissolves. 

 The four segments arrange themselves in the equator between the 

 two centrosomes in the manner described above, whilst a dis- 

 tinct radiation develops around the centrosomes in the proto- 

 plasm, so that the appearance, seen from the pole, resembles that 

 depicted in Fig. 85 A. The four segments then split longitudinally 



A B 



Fig. 85.-4 Four mother-segments seen from the pole of the nuclear figure (after van 

 Beneden and Neyt, PI. VI., Fig. 16). B Longitudinal splitting of the four mother-seg- 

 ments into eight daughter-segments (after van Beneden and Neyt, PI. VI., Fig. 17). 



that is to say, the third stage commences (Fig. 85 B). The 

 daughter segments thus formed separate from one another, and 

 travel towards opposite poles. E. van Beneden (VI. 4b) and Boveri 

 (VI. 6) consider that the spindle fibrils play an active part in this 

 process. In their opinion, the spindle in Ascaris is composed of 

 two independent portions, each of which consists of a large 

 number of protoplasmic fibrils. These 

 converge towards the centrosome and 

 attach their ends to it, whilst the op- 

 posite ends diverge, approach the nuclear 

 loops, and fasten themselves at various 

 points to the daughter-segments, which 

 are turned towards them. These threads 

 by gradually contracting, and thus be- 

 coming shortened, cause, in van Beneden's 

 and Boveri's opinion, the separation of 

 the four daughter-segments, which are 

 thus gradually drawn towards the cen- 

 trosomes. 



Fig. 8G. The construction 

 of the spindle out of two half- 

 spindles, the fibrils of which 

 have attached themselves to 

 the daughter-segments. (After 

 van Beneden and Neyt, PI. 

 VI., Fig. 8.) 



