238 THE PHYSIOLOGY OF REPRODUCTION 



paper 1 the reader is referred. It is shown that the ovum of the 

 sea-urchin, under an appropriate stimulus, is able to construct the 

 complete mechanism of mitotic cell division without the importation 

 of a sperm-centrosome, but beyond this a multitude of aberrations 

 are exhibited. The number of chromosomes is one-half that 

 occurring in normally fertilised eggs, being in the sea-urchin 

 eighteen instead of thirty-six. The centrosomes are primarily 

 formed df. novo. According to Delage, 2 however, the number of 

 chromosomes in artificially fertilised sea-urchins becomes eventually 

 restored to the normal by a process of auto-regulation. 



1 "VVilson (E. B.), " Experimental Studies in Cytology : I. A Cytological Study 

 i if Artificial Parthenogenesis in Sea- Urchin Eggs," J /<//. f. Entwick.-Jfechanii, 

 vol. xii., 1901. For an account of the cytojogical phenomena in normal 

 parthenogenetic eggs, especially in insects, see Hewitt, " Cytological Aspects 

 of Parthenogenesis in Insects," Memoirs and Proc. Manchester Literary <>// 

 /'/,i/<i.<t,/>/,;,-n/ >sy., vol. 1., 1906. 



2 ,Delage, "Etudes experimentales sur la Maturation Cytoplasmique chez 

 les Echinodermes," Arch, de Zoot. A'./y //'/. >'f <i*'n., vol. ix., 1901. Cf. also 

 Tennent and Hogue, "Studies on the Development of the Starfish Egg," 



/-. ,,/' A'./y/. Zt>/., vol. iii., 1906. 



