320 Elliot R. Downing, 



are obscured by the presence of the chromatin that the nucleus 

 excludes; Fig-. 23, Plate 12 gives a common appearance. The chromo- 

 somes are irregular, as Brauer shows them and the chromatin 

 granules make accurate observation difficult. It is onlj^ occasionally, 

 perhaps at some particular stage, that one sees the rod shaped 

 chromosomes clearly and can make out their structure. What stages 

 I have been able to find are so evidently homologous with those of 

 the spermatogenesis that it is probable that the others will be found 

 closely similar. There is this difference apparent, however, the 

 chromosomes in the oocytes are rod shaped while in the divisions 

 of the spermatocj'tes they appear spherical. I pointed out in the 

 paper on the spermatogenesis that the chromosomes of the inter- 

 stitial cells imbedded in the tissue are rod shaped; it is only in 

 the spermary, where the cells are relieved from pressure that the 

 form of the chromosome becomes altered. In the oocytes, where the 

 mitosis occurs under the pressure of the crowded cells, the rod 

 is maintained. The fact of the similarity in shape of the chromo- 

 somes in the oocytes and in the ordinary interstitial cells is evident : 

 the suggested explanation is hypothesis. 



37. The six chromosomes of the second polar spindle divide 

 longitudinally and six chromosomes go to the egg and also to the 

 second polar body, each chromosome being composed of four chromo- 

 meres. In this respect, also, there is a difference between the ovo- 

 genesis and the spermatogenesis. The chromosomes of the spermato- 

 cytes of the second order contain four chromomeres; but on division 

 the chromosomes going to the spermatids have only two chromo- 

 meres each. The comparison makes it evident that the two chromo- 

 meres of the spermatid chromosomes are bivalent, a conclusion to 

 which I came in the paper on the spermatogenesis, p. 407 and which 

 seems justified by the present facts. There is no evidence, that the 

 second division is a reduction division. 



38. The telophase of this second polar spindle is prolonged, 

 lasting through the extrusion of the egg and until fertilization 

 occurs. Meanwhile this female pronucleus is growing rapidly. It 

 lies below a crater-like depression in the cytoplasm of the egg: 

 this was seen by Brauer but in his figures it is shown in later 

 stages when it is disappearing. Fig. 24 and 25, Plate 12 show this 

 depression and the male and female pronuclei. 



On the whole one is impressed, in a study of the ovogenesis of 

 the hydra, with the independence of the egg and its antagonism 



