346 B. F. KINGSBURY 



among the higher forms, up to and inckiding man, is regarded as 

 supporting this contention. On this interpretation the indifferent 

 period would be a potentially bisexual or hermaphroditic period 

 in development. This interpretation is not necessarily opposed 

 to the view that the sex-determining factors are already present 

 in the egg at the time of its fertilization. (2) As a modification 

 of the above view might be mentioned the interpretation that the 

 early mammalian embryo during the indifferent period is truly 

 bisexual, containing the potentialities of either sex whose subse- 

 quent determination leads to the arrest, atrophy and more or 

 less complete disappearance of the organs of the opposite sex. 

 These two views are related and also bear on the problem of sex 

 determination whose cytological side is subsequently mentioned 

 and briefly discussed. (3) It has been argued that the reason 

 for the development of the Mullerian duct in the male is due to 

 the fact that it was the original reproductive duct and that the 

 utilization of the excretory duct system in the male as a repro- 

 ductive duct was a secondary acquirement. This interpretation, 

 supported by Waldeyer and Lenhossek, hardly suffices. The 

 theory would fail to explain the appearance of the rudimentary 

 mammary gland in the male, or the prostate and rete ovarii in 

 the female. (4) The converse of this view might be suggested, 

 namely, that the pronephric duct system (the male duct system) 

 represented the ancestral system in the nephridia in pre-chordate 

 forms, serving not only the nephric system but the reproductive 

 system as well, and conveying both the male and female repro- 

 ductive cells to the exterior. The shedding of the female repro- 

 ductive cells into the coelomic cavity from the surface of the 

 gonad and the development of a Mullerian duct in association 

 therewith would thus be a secondary adaption.^ (5) By no 

 means exclusive of the preceding suggestions as to the meaning 

 of the double character of the reproductive organs, since tfiey 

 deal with a distinct aspect of the problem, should be mentioned 



1 Cf. Felix, W. ; Theoretische Betrachtungen uber das Genitalsystem der Verte- 

 braten. pp. 821-834, Handbuch der Entwicklungsgeschichte der Wirbeltiere, Vol. 

 3, 1, 1906. 



