Mr M c Dowall, A Preliminary Note, etc, 311 



nuclear membrane, and there it is immediately disintegrated. 

 The maturation-divisions themselves are difficult to follow. 



The deutoplasm is exceedingly dense* at this time, and often 

 appears to contain fragments of the degenerated nucleolus, so that 

 the details are much obscured. Additional difficulties arise, owing 

 to the fact that the first maturation-division only takes place at 

 or just before the time of the entrance of the spermatozoon, the 

 second immediately succeeding it ; while definite polar bodies are 

 not formed, the polar nuclei remaining in the deutoplasm. The 

 divisions, however, appear to be of the normal type*f", the double 

 chromosomes splitting into their components and six going 

 into the first polar body, which may again divide subsequently, 

 the other six at once splitting along the already-formed line of 

 fission. Thus the first division is a reduction. I have not been 

 able to distinguish any definite spindle-fibres. This may be due 

 to the density of the deutoplasm, or possibly to imperfect preserva- 

 tion, although the earlier stages are perfectly preserved. By 

 using an oblique illumination, distinct lines of stress in the deuto- 

 plasm are sometimes made visible, so that it is quite possible that 

 no actual fibres are formed. 



The male nucleus is small, but very rapidly enlarges in its 

 passage through the ovum. The chromosomes of the male and 

 female nuclei perhaps unite in pairs, temporarily. Distinct indi- 

 cations of such a pairing are to be found. 



The nucleus then enters on a densely-chromatic resting-stage. 

 It is extremely large. 



A large centrally-placed nucleolus appears, and the chromatin 

 arranges itself round this in a very characteristic manner. The 

 yolk rapidly increases, and acquires a different reaction, spherules 

 being present which stain well with haematoxylin ; whereas before 

 fertilisation spherules were not recognisable, and the deutoplasm 

 stained with orange G. 



It may be worth noting here what very different results are 

 obtained by using unsatisfactory preservatives. A series of 

 fertilised ova, preserved with Flemming's fluid and stained with 

 iron-haematoxylin and eosin, show a very distinct nuclear mem- 

 brane, surrounding a clear space which stains rather unevenly 

 a yellowish colour, in which lie two definite structures of large 

 size, one curved and dark, the other a cloudy reflection of the first, 

 staining a brownish colour. 



* Cf. C. Neuhaus, Jenaisehe Zeitschr. filr Naturwiss., Bd. xxxvu. p. 653. 



f I can find no trace of the persistence of the double-chromosomes described by 

 K. Bonnevie in Enteroxenos [op. cit.). Bather, the evidence distinctly points to a 

 separation of the conjugated chromosomes, though whether this actually occurs in 

 the first or the second maturation-division is difficult to determine, owing to the 

 symmetrical tetrad form of the double-chromosomes. 



