GROWTH AND REPRODUCTION 781 



continuous leaps and bounds by " mutations." "The new species 

 appears all at once ; it originates from the parent species without any 

 visible preparation, and without any obvious series of transitional 

 forms." This is the mutation theory of De Vries. 



It would seem, then, that the distinctive characters of a species 

 may arise in two ways: (1) By the accumulation of fluctuations; 

 (2) suddenly by mutation. 



The extent to which the acquired conditions of environment are 

 transmitted, if at all, still remains to be settled. That such environ- 

 mental condition? are of great importance is indicated by experiments 

 upon bacteria. It is known that virulent organisms may be attenuated 

 by growths upon special media, and that such diminution of virulence 

 is maintained so long as the environmental conditions remain the 

 same. This would point strongly to the conclusion that the effects 

 of the environment of the race induced by improved conditions may 

 be maintained in the offspring so long as the better environmental 

 conditions are maintained. Herein lies the great hope of the 

 humanitarian. 



The Determination of Sex. The determination of sex has long 

 been a matter of popular speculation, but only recently of scientific 

 inquiry. In consequence, many theories, although of historic interest, 

 are scarcely of scientific value. Such, for example, are the views that 

 sex is determined by parental desire; by the element of the more 

 healthy parent ; by the relative age of the parents ; by the relation of 

 coitus to menstruation; or whether the ovum comes from the right 

 ovary or the left. 



It is generally believed, and to a certain extent it is supported 

 by statistical evidence, that more male babes are born in and after 

 times of stress, such as war and famine. The disproportion between 

 the sexes (women are more numerous) is to some extent accounted 

 for by the more difficult passage of the male babe into the world, 

 owing to his larger head, and to the more precarious occupation of 

 males in the community. 



In recent lines of inquiry, efforts have been made to ascertain 

 whether sex is predetermined in the sexual elements, or whether 

 sex is determined by environmental conditions of the ovum after 

 fertilization. Evidence has been accumulated in favour of both 

 views. In support of the environmental view, it is claimed that 

 well-matured frog's spawn develops into an excess of females, and that 

 ill-matured eggs of certain caterpillars yield an excess of males. 

 Differences of temperature, by affecting the nutrition of the mother, 

 have been shown to exert an influence upon the sex of the 

 offspring of the primitive worm Dinophilus. An experiment of 

 great interest is one upon the annelid worm Ophryotrocha 

 puerilis. When a female of this species, with no trace of hermaph- 

 roditism, having ripe ova, was divided into two, the head portion 

 of thirteen segments regenerated seven segments, and, on being killed, 

 it was found that the ova and female apparatus had atrophied, and 

 that the animal was now male, with a functional testicular portion 



