58 CALIFORNIA ACADEMY OF SCIENCES. 



objection, as the subject is still under discussion. Cer- 

 tain it is, however, that the replies which have been 

 made by Poulton and Trow are incorrect and Hartog 

 demonstrates their inconsistency with the views of Weis- 

 mann by a letter from that gentleman. 



Lloyd Morgan suggests as an hypothesis of variation 

 a modification of Spencer's theory of physiological units, 

 which has much to commend it, viz., the organic com- 

 bination of the elements of the two sexes into a specific- 

 ally new compound. Morgan explains the need of this 

 hypothesis as follows:* '' * '^ * if, in sexual union, 

 there is a mere mixture, a mere commingling of heredi- 

 tary characters, it is quite impossible that new characters 

 should result, or any intensification of existing charac- 

 ters be produced beyond the mean of those of ovum and 

 sperm. -^^ * -^ Let us suppose, for the sake of illus- 

 tration, that a pair of organisms have each an available 

 store of forty units of growth-force, and that these are 

 distributed among five sets of organs, a to e, as in the 

 first two columns. Then the offspring will show the 

 organs as arranged in the third column. 



40 40 40 



" There is no increase in the set of organs a, which 

 are strongly developed in both parents; and no decrease 

 in the set of organs e, which are weakly developed in 

 both parents. By sexual admixture alone there can be 

 no increase or decrease beyond the mean of the two 



* Animal Life and Intelligence, pp. 150, 151. 



