ARTIFICIAL PARTHENOGPJNESIS AND FERTILISATION. 481 



nuclear sap set free from the germinal vesicle, is accompanied 

 by the conversion of the large vesicular nucleus related to the 

 metabolic changes underlying the growth of the ovum, into a 

 small morphologically equivalent nucleus, possessing the same 

 number of chromosomes as the sperm nucleus. This has been 

 proved by their enumeration when the nuclei undergo in- 

 dependent transformation, and the number is one half that 

 found in the segmentation divisions. 



The eggs thus matured remain, in the case of the sea-urchin, 

 for a considerable time quiescent within the ovary before they 

 are discharged — for the process of ripening in the ovary 

 is a gradual one. When discharged into sea water it seems 

 that, like the eggs of some other forms (0. Hertwig, 1893, 

 p. 239), after lying for many hours unchanged, the sea- 

 urchin eggs show spontaneously, karyokinetic transforma- 

 tion ; for instance, R. Hertwig (1896) observed in eggs which 

 had been deposited prematurely during transport, analogous 

 changes to those produced by treatment with strychnine. 

 This phenomenon is one apparently of wide range. In an 

 interesting review entitled " Giebt es bei Wirbeltieren Par- 

 thenogenesis " (1900), Bounet, after examination of all the 

 literature up to that date, comes to the conclusion that, 

 according to our present knowledge, the phenomena in verte- 

 brates are due to degenerative divisions, and in meroblastic 

 eggs to fragmentations, and the alleged parthenogenetically 

 divided tubal, uterine or laid eggs, are either over-ripe, and 

 therefore badly fertilised, or are eggs normally fertilised 

 with defective spermatozoa. In the light of the facts of 

 artificial parthenogenesis, it may be that this segmentation 

 in unfertilised eggs, at least in certain invertebrates, is an 

 effort in the direction of true parthenogenesis which is abor- 

 tive, the egg dying before the tardy process is accomplished. 



In 1876 Greeff described parthenogenetic development in 

 Asterocanthion. The eggs were obtained from animals 

 early in the season, before the spermatozoa were mobile, and 

 the blastulaj formed differed from those produced in normal 

 fertilisation. 0. Hertwig (1890) recorded some observations 



