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 de novo. According to Delage,^ however, the number of 

 chromosomes in artificially fertilised sea-urchins becomes eventually 

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



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

 of Artificial Parthenogenesis in Sea-Urchin Eggs," Arch. f. Entwick.-Mechanii;, 

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

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

 of Parthenogenesis in Insects," Memoirs and Proa. Manchester Literary and 

 Philosophical Soc., vol. 1., 1906. 



2 Delage, " Etudes exp6rimentales sur la Maturation Cytoplasmique chez 

 les Echinodermes," Arch, de Zool. Exper. et Gen., vol. ix., 1901. Cf. also 

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

 Jour, of Exp. Zool., v;ol. iii., 1906. 



