154 SCIENCE PROGRESS. 



the poles move farther apart, though whether owing to a 

 stress in the now continuous axile strand or whether owing 

 to the strain caused by the contraction of the peripheral 

 fibres which run out to the cell wall, it is impossible to say, 

 It suffices for present purpose that here, too, as in the Sala- 

 mander, the triangular character disappears, and the chro- 

 mosomes are pulled to the axile strand, on which they 

 proceed to undergo division in the usual way. In other 

 plants there is not such an obvious formation of a central 

 core of fibres, but in reality it is probably of common oc- 

 currence, and a form of it can with certainty be distinguished 

 in many cells ; that is to say, some fibres may be seen to 

 run right across from pole to pole, while others only run 

 from the pole to the chromosomes. The final result is the 

 chief thing, the actual method followed being subject to 

 indefinite variety in detail, depending doubtless on the 

 local conditions existing in the cell. 



Again, the spindle, at any rate the part of it which 

 lies between the two poles, may be entirely of nuclear 

 origin, and it thus stands in sharp contrast with such a 

 form as that existing in the Salamander. This kind of 

 spindle occurs in Ascaris vieg. var. imivalens, in which 

 the centrosomes are also intranuclear, also in the sper- 

 matogenic divisions in some birds, as was noticed by 

 Moore a year ago. In plants it occurs in some fungi ; 

 in algae Fairchild observed it in Valonia} and it also 

 occurs in FiLms. In the latter plant, indeed, it can readily 

 be seen to arise within the nucleus, as the result of a d'f- 

 ferentiation of the achromatic substance, and the division 

 of the chromosomes occurs while the orio-inal nuclear wall 

 is still unbroken. This, to my mind, is strong evidence 

 against the existence of any special spindle-forming sub- 

 stance, which is postulated by some writers. I believe the 

 spindle to be nothing more than a differentiation in the pre- 

 existing protoplasm, and I see no need to further complicate 

 a matter already sufficiently brisding with difficulties by in- 



1 Fairchild, "Ein Beitr. z. Kenntniss d. Kernth. li. Valonia i/tticu/aris," 

 Ber. d. D^utscti. hot. geseti., xii. 



