592 SCIENCE PROGRESS 



until some of the difficulties in its way have been surmounted. 

 One of the most conspicuous of these, as Prof. Correns has 

 pointed out, is offered by the facts of hermaphroditism ; and 

 they seem indeed to give basis for a serious objection to the 

 quantitative interpretation. The puzzle is, however, not more 

 baffling than that presented by the heredity of such characters 

 as the mottled or piebald types of colour-patterns under the 

 presence and absence theory; and possibly an explanation of 

 the latter case will give a clue to the nature of the former. 



But space forbids further discussion of this point. We 

 return from our excursion into the theoretical field compelled 

 to admit that the data for an adequate or definitive general 

 interpretation of sex are not yet at our command. Cytological 

 research has nevertheless made a substantial advance towards 

 the solution of the problem. The cytological phenomena that 

 have been described have already led to a better understanding 

 of sex-production ; and the concrete results of observation must 

 not be confused with any of the theoretical interpretations that 

 we may place upon them. Phenomena of this kind seem likely 

 to throw further light on the mechanism of Mendelian heredity 

 as well as of sex-production, for they demonstrate a disjunction 

 of different elements in the formation of the gametes; and this 

 again is a fact, not a theory. 



