BO VERIRABLFOL 



261 



reason of their " power of lengthening and shortening themselves, 

 be characterised as muscular fibrillae, and all the laws that obtain 

 for muscles might be applied to them " (ii. p. 99). After such 

 an opinion it seems astonishing when Boveri defends (ii. p. 80) 

 on the other hand the view, or at least declares it to be the most 

 probable one, that the fibrils of the aster do not permanently 

 exist as such in the protoplasm, and that they are not, as van 

 Beneden and others correctly recognised, produced from the 

 meshes of a framework existing in the protoplasm, but that they 

 are first formed ad hoc by connection of the otherwise separate 

 microsomes of the archoplasma. As far as I understand Boveri, 

 he seems to represent the view that it is especially the microsomes 

 of the so-called archoplasma, i.e. of the so-called central areae, 

 that produce the filaments, which then commence to grow from 

 the archoplasm outwards into the surrounding protoplasm by 

 elongation. I scarcely think that any one will be strongly in 

 favour of this view, according to which alleged muscle fibrils 

 arise at one time from the union of microsomes, and at another 

 time break up again into such bodies. 



Rabl (1889) has recently fallen in with the interpretation of 

 the systems of rays as contractile fibrillae, which play in cell 

 division the part assigned to them by van Beneden. He assumes 

 that the framework of the cell protoplasm and nucleus is per- 

 manently centred round the central corpuscle a view which is 

 in fact favoured by observations upon the radiate arrangement of 

 the protoplasm round the central bodies of certain resting cells. 

 He is further inclined to believe that the reticular framework 

 of the protoplasm is transformed into fibrils during division, like 

 those of the nucleus, by a breaking up of the cross connections of 

 the filaments ; consequently the systems of rays only consist of 

 isolated fibrils, which later become modified again into networks 

 by the formation of anastomoses. 



Finally, Fol has attempted recently (1891) to demonstrate in 

 the egg of the sea-urchin a different mode of formation for the 

 radiations which appear primitively round the sexual nuclei and 

 the segmentation nucleus derived from them, and for the so- 

 called suns or asters at the poles of the nuclear spindle. The 

 former are stated to depend only on the arrangement of the yolk 

 granules and of the " tracts of sarcode " by which they are sus- 

 pended. The true asters, on the other hand, are formed of 

 actual rays, i.e. fibrillae which are just as distinct and capable of 

 being isolated as the connective tissue and muscular fibrils. I 

 am unable to agree at all with this view, either from my own 

 observations, or from the experience of other investigators. The 

 possibility of isolating the fibrils is not, in my opinion, in any 



