248 



The Journal of Heredity 



determination and sex-differentiation. 

 Sex may ^ be determined j^enetically 

 by the chromsomes at the time the e^g is 

 fertilized, but may be altered more or 

 less completely by a chanj^e in the hor- 

 mones. The chromosome mechanism 

 appears to give a strong,' initial impulse 

 toward a certain sex, and the hormone 

 mechanism carries this imjjulse for- 

 ward to completion. But if the hor- 

 mone mechanism is reversed, the initial 

 impulse of the chromosomes may be 

 overcome, and the animal which should 

 have become a female will become the 

 equivalent of a male, or vice versa. 



IS TWINNING HEREDITARY? 



In the Texas armadillo it goes with- 

 out saying that twinning is hereditary; 

 it is the only mode of reproduction 

 in this species. What is really inherited 

 in this case is not fully understood, but 

 it is believed that its basis lies in some 

 physiological peculiarity of the egg, 

 which causes it to have an abnormally 

 slow early develojjment. As noted 

 above, this retardation in the develop- 

 mental rhythm produces an early fission 

 in the embryonic mass and starts sepa- 

 rate development at four different points. 



The case is not so clear in other 

 mammals. The experiments of Alexan- 

 der Graham Bell suggest that twinning 

 is to some extent hereditary in sheep, 

 Init other studies have failed to find good 



evidence of this. All the work that 

 has so far been done on the inheritance 

 of fecundity in mammals has yielded 

 ver>' small results. In man, twinning 

 appears to be hereditary* to some extent, 

 and it seems jjossible that the tendenc\' 

 to produce identical twins may be trans- 

 mitted through the father as well as the 

 mother. The tendency to produce ordi- 

 nary fraternal twins is, of course, a func- 

 tion of the mother solely, since it de- 

 pends on the production of two ova at 

 once. But the details of the inheritance 

 of twinning are extremely obscure. 



HEREDITY IN THE ARMADILLO 



If the character of an individual were 

 determined wholly by heredity, the 

 armadillo quadruplets ought to be cor- 

 related perfectly. As a fact, they are 

 found to be correlated to the extent of 

 about .92. But this is what is to be 

 expected, since room must always be 

 left for irregularities in development. 

 Even a bone in a man's leg is not per- 

 fectly correlated with the corresponding 

 bone in his other leg, the coefficient 

 being .97. It is evident, then, that while 

 the pattern of the armor (the particular 

 character studied in this case) is largely 

 determined by heredity, there is some 

 irregularity due to differences in devel- 

 opment; but that in the case of these 

 identical quadruplets, heredity* is nine- 

 tenths responsible for the individual. 



Unemployment and Feeblemindedness 



That feeblemindedness is an im- 

 jjortant factor in unemjjloNTnent is the 

 conclusion of Glenn R. Johnson, who 

 applied tests to a re])re.sentative groujj 

 of 107 unemployed men who ap]jlied 

 for charity in Portland, Ore. He con- 

 siders that about one-fifth of the desti- 

 tute men in Portland (and jjrobablj' in 

 other cities on the Pacific Coast) are 

 high-grade morons, and as a group all 

 the destitute men were considerably 

 inferior inentally to an ordinary grouj) of 

 successful men. Me found there was no 



relation between wildness in youth and 

 intelligence, and that extreme dissipa- 

 tion did not seem to affect the intelli- 

 gence level of some men. His conclu- 

 sions are reported in the Journal of De- 

 linquency, March, 1917. His findings 

 bear out the conclusions of other investi- 

 gators, that many of the men who are 

 "down and out" are not there because 

 they have never been given a chance, 

 but because they are inherently incap- 

 able of utilizing a chance giv^en to 

 thtm. 



* The best concise account is in the Joiknai. hi- ill- i<i;i»i rv, vii. p]). 105-202. May, 1916; Is 

 Twinning Hereditary? by C. H. Danforth. 



* It must be said that Professor Newman's discus^on of heredity is not beyond criticism: 

 e. ^., the statement (p. 124) that both kinds of twinning in mammals "are characters capable of 

 bemg inherited as unit characters." 



