692 THE PHYSIOLOGY OF REPRODUCTION 



ia the ovaries, and that this so alters the general nutritive conditions 

 in the direction of the female sex that eventually ova are formed in 

 the gonad. On this view the yolk substance is produced in response 

 to a stimulus set up by the parasite. 



Braem^ has described an experiment in which he divided into 

 two parts a mature female of Ophryotrocha puerilis. After some weeks 

 the head portion regenerated and produced spermatozoa, but the ova 

 almost disappeared. There was no sign of hermaphroditism at the 

 outset, and Braem regards the case as one of change of sex resulting 

 from the altered conditions. 



Orton ^ states that in the mollusc Grepidula fornicata the males 

 under certain conditions may change into females, thus showing that 

 they have the potentialities of both sexes. The life history of this 

 mollusc has been further investigated by Gould,^ who shows that 

 the free swimming young, after settling upon older individuals, pass 

 through a series of sexual changes. First they pass through a 

 neutral phase, next they develop into males ; then they change ' 

 into hermaphrodites, and lastly become females. In Grepidula plana, 

 the individuals only become males if attached at or near a larger 

 individual; otherwise they become females without any transition 

 from the neutral condition. 



The marine annelid Bonellia displays similar phenomena. The 

 larvse, after being free swimming, become attached to the sea bottom . 

 and develop through a neutral phase into females, or else they establish 

 themselves upon the proboscis of a mature female and become males. 

 Baltzer,* by releasing such larvse before their sex had become com- 

 pletely established and forcing them to lead an independent life, 

 was able to produce grades of intersexual individuals, in which the 

 degrees of malehess or femaleness depended upon the duration of 

 time on which they had been attached before being released. 



Potts ^ has adduced evidence that in certain hermaphrodite 

 Nematodes, in Ehabdocoel Turbellarians and in Bhizocephala the 

 monoecious condition has arisen through the spermatozoa developing 

 in the ovaries in gradually increasing numbers in successive generations. 



Champy ^ has described some interesting experiments on newts, 



1 Braem, " Ueber die Aenderung des Geschlechts durch aussere Beeinflussung, 

 etc.," Anat. Am., vol. xxxiii., 1908. 



^ Orton, " On the Occurrence of Protandric Hermaphroditism in the Mollusc 

 Crepidula fornicata," Proc. Roy. Soc, B., vol. Ixxxi., 1909. 



^ Gould, " Studies on Sex in the Hermaphrodite Mollusc Crepidula plana,'\ 

 Jour, of Exp. Zool., I., II., and III., vol. xxiii., 1917, and vol. xxix., 1919. 



* Baltzer, "Die Bestimmung des Geschlechts nebst einez Analyse des 

 Geschlechtsdimorphismus bei Bonellia," Mith. Zool. Stat. Neapol., vol. xxii., 1914. 



^ Potts, " Notes on the Free-living Nematodes," I., (iimr. Jov/r. Micr. Science, 

 vol. Iv., 1910. 



° Champy, "Ghangement experimentelle du Sexe chez le Triton alpestris," 

 C. R. de VAcad. Sci., vol. clxxii., (9th May) 1921. (See also footnote, p. 700.) 



