DAUWIX. BEFORE AND AP^TER i7:^ 



or tissue, such as the reproductive organs, tlie jiancreas, 

 the thyroid gland aud actively jijrowinj*- tissues. Ilor 

 mones '^ are produced in one organ, and carried by tht^ 

 blood to another organ, on which their etfect is niani 

 fested." According to Cunningham, external stimula- 

 tion may affect certain hormones, and tliey, in turn, may 

 influence the gonads, producing modifications of the cor- 

 responding parts of the offspring. Support is said to 

 be given to the hormone hypothesis by observations on 

 secondary sexual characters in animals, though Oeoffrey 

 Smith interpreted such characters otherwise. The de- 

 velopment of antlers in the male deer would be the result 

 of a cliemical stimulus originating in the male organs, 

 which, by acting on the skull, causes the inherited ten- 

 denc}' to the development of antlers to become active. An 

 example of the disturbance of hormones is afforded by 

 the cretin, whose thyroid gland is diseased, and to whom 

 the administration of thyroid extract, containing thyroid 

 hormones to supply the deficiency, causes an increase in 

 mental and physical development. The hormone hypo- 

 thesis affords an explanation of the Lamarckian principle 

 of the inheritance of acquired characters. Perhaps may 

 be mentioned here the recent, interesting experiments of 

 Julian Huxley, who induced metamorphosis 'of the Mexi- 

 can larval Amphibian, known as the Axolotl, by the use 

 of thyroid extract. Further experiments and explana- 

 tions on this subject are awaited. 



Sir Francis Galton formulated a hypothesis of an 

 cestral inheritance. With Weismann, he assumed the 

 continuity of the germ plasm, and figured mathematically 

 the amount contributed by each generation to the make- 

 up of one given individual. In other words, by statistical 

 methods he estimated quantitatively the characters in a 

 number of successive generations. A near ancestor be- 

 queathed to the individual more elements than a remote 

 ancestor. The series has been slightly modified by Pro- 

 fessor Karl Pearson, and there has been much statistical 



