THE VITAL PHENOMENA OF THE CELL 



201 



Fig. 95. Construction of 

 the spindle out of two half- 

 spindles, the fibrils of which 

 are attached to the daughter- 

 segments. (Front van Bener 

 den and Neyt, PI. VI. , Fig. .) 



to its construction and origin. Whilst the first observers considered 

 that the spindle consisted of most delicate fibrils, which stretched 

 continuously from pole to pole, van Beneden (VI. 46) and Boveri 

 (VI. 6) are of opinion that these fibrils are broken at the equator, 

 and that, in consequence, the spindle is 

 composed of two separate and distinct 

 half-spindles (Fig. 95) . They contend that 

 the half-spindles are attached directly 

 with the ends of their fibrils to the nu- 

 clear segments, and in consequence are 

 of mechanical use in nuclear division, in 

 that they shorten or contract like muscle 

 fibres after the segments have divided 

 into daughter-segments, and thus draw 

 the daughter-segments, which are at- 

 tached to them, in opposite directions. 



On the other hand, Flemming (VI. 14) for the tissue cells of 

 Salamandra, and Strasburger (VI. 72) for plants, still adhere to 

 their old theory, that spindle fibrils, stretching uninterruptedly 

 from pole to pole, do exist. The observations made by Hermann, 

 which have been already mentioned, are especially convincing 

 concerning the undivided condition of the spindle ; they call 

 to mind my description and representation of the formation of 

 the spindle in the germinal vesicle of Asteracantliion (VI. 30a, 

 PL VIII., Figs. 3, 4). In both cases a very small, undivided 

 spindle may be observed between the poles, which are situated 

 near to one another (Fig. 96), at that period when the nuclear 

 segments are a good way 

 off, and so cannot hide it 

 at all ; it is seen to grow 

 gradually, as its fibrils in- 

 crease in length, until it 

 reaches its full size. 



The explanation of this 

 discrepancy, as has been 

 suggested by Hermann, is 

 that the structure described 

 by van Beneden and Boveri 



as the half-Spindle is some- Fig. 96. Nucleus of a sperm-mother-cell of 



thing quite different from Salamandra maculate preparing to divide. Posi- 



tion of the spindle between the two centrosomes. 



the spindle of the earlier (After Hermann, PI. XXXL, Fig. 7.) 



