498 TUOMAS n. butcr. 



Regarding tlie main point, it may be admitted that tlie 

 astei" and its centrosome here concerned is that belonging to 

 the sperm nucleus, and that in its behaviour we have a 

 beautiful demonstration of the independence of the two 

 factors in fertilisation^ or, in other words, of the two func- 

 tions of the spermatozoon, and that the two functions have 

 been disturbed in unequal degree. At the same time the 

 egg protoplasm, after the fourteen hours' sojourn iu 

 unrenewed sea water, was approaching to that stage iu 

 which it acquires spontaneously the tendency to develop 

 astral activities, and it might be held that the coudiLions are 

 the same as in magnesium eggs in which, as a result of a 

 general stimulation, asters and centrosomes which are 

 unconnected with the nucleus appear de novo in the 

 cytoplasm. While the results are of interest in connection 

 with the apparent independence of the factors in fertilisation, 

 they also show how they are co-ordinated together. The 

 sperm nucleus becomes dissociated from the aster, and fails of 

 union, because it has not undergone the transformation which 

 properly corresponds to the phase reached in the cycle of the 

 centrosomal changes. Furthei-, while the nuclei may be re- 

 solved into chromosomes before union, and yet unite in the 

 equatorial plate stage, a certain stage in the transformation 

 of the dense mass of chromatin of the sperm head into 

 a nucleus with distinct chromatin network, must be reached 

 before union can take place. This seems to show that several 

 co-ordinated factors are at work in the nuclear conjugation. 



Further insight into the behaviour of the factors iu 

 fertilisation is given by an experiment described by Ziegler 

 (181)8). This consisted in carrying newly-fertilised eggs by 

 a gentle current of water in his compressorium against 

 threads of cotton wool. The egg was caught on a thread 

 and nearly cut through, leaving only a slender bridge of 

 protoplasm between the two portions of the egg. The one 

 contained the sperm nucleus, the other the germ nucleus. 

 While the sperm nucleus regularly divided, followed by 

 division of the cytoplasm, the egg nucleus merely underwent 



