MARK— KLEIN— VAN BENEDEN 259 



by a mixture of two substances, one of which was derived from 

 the nucleus, the other from the protoplasm. 



Mark, in 1881, criticised the Adews of earlier investigators 

 upon the cause of the aster formation very ably indeed, without, 

 however, expressing a definite opinion himself upon their signi- 

 ficance. Thus he remarks, on the one hand (p. 533), " While I 

 concur with Hertwig in the belief that there is an attractive force 

 exerted upon the vitelline protoplasm which emanates from the 

 centre of radiation," and, on the other hand (p. 530), "I do 

 not claim that there is absolutely no transfer of substance to and 

 from the centres of attraction. On the contrary, I believe the 

 phenomena are, on any other assumption, unintelligible ; but it 

 seems to me that the formation of a clear area, and the existence 

 of radial striations, are far from commensurate, and that to claim 

 that the rays are only the optical expression of currents is to 

 associate as cause and efiect two things which have not neces- 

 sarily any such connection with each other." The view expressed 

 by me he also regards not as a real explanation, but more as a 

 description of the phenomenon. I can only accept this criticism 

 to the extent that I did not indeed give an explanation in the 

 mechanical sense, which, however, was not my intention, but I 

 think, on the other haiid, I established certain conditions under 

 which the phenomena make their appearance. For the rest, 

 Mark has understood my view very correctly, and since this was 

 not always the case I will quote here his remarks upon this 

 point (p. 530) : "Biitschli's opinion that the asters are the optical 

 expression of a physico-chemical alteration of the protoplasm 

 emanating from the central area is probably incontrovertible. 

 At least there is a physical alteration of the protoplasm, and 

 it first becomes apparent at the centre of the star ; but this is 

 rather a description than an explanation of the appearance." 



Klein had already (1879 (2), pp. 416, 417) casually expressed 

 the opinion that the striations round the poles of the dividing 

 nucleus only depend on a particular arrangement of the proto- 

 plasmic network, since the nuclear network probably contracts 

 during the nuclear division, and draws the protoplasmic fibres 

 towards itself. It is strange that Klein did not come to exactly 

 the reverse idea, which would have corresponded much more to the 

 processes actually taking place, and which, therefore, soon came to 

 be held. Nevertheless, we must recognise that he first pointed 

 out the probable origin of the radiation by rearrangement of the 

 protoplasmic framework. Flemming, in 1879, while he admitted 

 the mechanical connection of the two processes brought into asso- 

 ciation by Klein, was yet inclined to regard the matter as not so 

 simple. In 1881 he pointed out in Towpneustes that the radia- 



