508 HEREDITY AND SEX 



F. Braem is very suggestive. He experimented with a simple 

 Annelid worm, Ophryotrocha puerilis. Taking a female which 

 had ripe eggs and showed no trace of hermaphroditism, he divided 

 it into two. The head portion, with thirteen segments, was 

 isolated. In three weeks it had regenerated seven segments with 

 parapodia. It was then killed and found to be male. The ova 

 had mostly disappeared from the reproductive organs, leaving 

 only a residue, and a functional testicular portion had developed, 

 which was producing spermatozoa. Braem suggests than in 

 consequence of the amputation the very young, indifferent 

 germ-cells had developed into male cells, which require less 

 subsistence than ova. What is certain is that the reproductive 

 organs had changed from producing eggs to producing sperms, 

 and such cases appear to us to favour the view that the sex- 

 difference is fundamentally physiological. 



In this connection Dr. F. H. A. Marshall remarks : " When 

 once we admit the existence of latent {i.e. recessive) sexual char- 

 acters in individuals in which the characters of one sex are 

 dominant, and that under certain circumstances those of the 

 latent sex can develop at the expense of the dominant ones, in 

 response to appropriate physiological stimuli, we are compelled 

 to acknowledge also that the sex of the future individual is not 

 always predetermined in the gametes or even in the fertilised 

 ovum, but may be called into being at a later stage in life." 

 The prevalent view to-day, that sex is irrevocably determined in 

 the germ-cells before fertilisation or in the fertilised egg-cell, 

 seems to be true in certain cases, but it is in itself too simple. 

 It requires physiological re-statement, and it requires the addition 

 of a number of saving clauses. 



It must be remembered that many at least of those who are 

 keenest on the scent of morphological criteria are also alive to the 

 importance of trying to get at the physiological realities behind 

 these. Thus we find Prof. Wilson saying, " Since the two classes 

 of spermatozoa differ in nuclear constitution, it is highly probable 





