932 SUMMARY OF CUERENT RESEARCHES RELATING TO 



the result may be sometimes due to nothing else than a certain increase in 

 the size of the nucleus. The authors have made numerous observations 

 with especial reference to the formation of double monsters, and they see 

 no reason to suppose that these are to be regarded as due to the fertilization 

 of one egg by two spermatozoa. 



Human Ovum.* — Dr. W. Nagel communicates a description of the 

 human ovum, in regard to which there has been a lack of precise informa- 

 tion. His material was obtained from ovaries removed in operations. 

 Healthy follicles were isolated and examined, and in other eases sectioned 

 in situ. 



The zona pellucida is very distinct, and is separated by an extremely 

 fine " perivitelline space" (apparently containing clear fluid) from the 

 vitellus. Within this is the narrow clear " cortical layer " of the vitellus, 

 then a somewhat broader finely granular " protoplasmic zone," then the 

 " deutoplasmic portion" with abundant globules, more abundant and less 

 refractive than in the ova of domestic mammals. 



The nucleus is round, clear, double-contoured, always excentric, and in 

 the protoplasmic zone. There is a distinct nuclear network. The 

 nucleolus exhibits amoeboid movements. 



The corona (epithelium of ovum) was always well developed on ripe 

 eggs. The diameter of the ripe ova varied from 124-128 ft. The various 

 zones vary somewhat in different regions. The nucleus measured 

 19-20 IX. 



In the ovaries of new-born subjects, besides the usual primordial 

 follicles, larger follicles were observed (Waldeyer-Slavjansky). In these, 

 sections revealed normal ova, and the author does not therefore regard the 

 presence of these large follicles as indicative of incipient cyst-formation. 



In development, the protoplasm and nucleus increase in size, the 

 follicular cells multiply, the deutoplasm is formed, the nucleus is pushed 

 to the side, and a zona pellucida begins to appear. 



Fertilization of Ovum of Lamprey.f — Herr A. A. Bohm has studied 

 the phenomena of fertilization in the ovum of Petromyzon planer i, and 

 gives the following summary of his results : — 



(1) The substance of the germinal vesicles spreads out on the surface 

 of the ovum at the animal pole to form the pole-plasma. 



(2) During impregnation, pari passu with the formation of the vitelline 

 membrane, the pole plasma is covered with a fresh, thick, folded membrane. 

 This concentrates the fertilization to a limited area, and disappears after 

 fertilization is accomplished. 



(3) The pole-plasma with the elements concerned in fertilization is 

 retracted inwards, but remains connected with the surface of a thin proto- 

 plasmic strand which lies in the axis of the ovum in the plane of the first 

 meridional segmentation. 



(4) The male and female nuclei fall into portions (spermato- and karyo- 

 merites). 



(5) For a while these can be microchemically distinguished. 



(6) The merites do not at first intermingle, but form two closely apposed 

 groups. The plane separating these two groups coincides with a meridian 

 of the ovum- 



(7) Each merite consists of a body with little chromatin and a body rich 

 in chromatin (the microsome). 



(8) The final nucleus of segmentation arises by the fusion of the 



* SB. K. Preuss. Akad. Berlin, 1887, pp. 759-61. 

 t SB. Bayer. Akad. Wiss. Munchen, 1887, pp. 53-62. 



