Vol. LI December, 1926 No. 6 



BIOLOGICAL BULLETIN 



INFLUENCE OF AGE OF MOTHER ON APPEARANCE 



OF AN HEREDITARY VARIATION 



IN HABROBRACON. 



P. W. WHITING, 



UNIVERSITY OF MAINE. 



Contentions about the inheritance of acquired characters have 

 frequently involved questions of the age of the parents. Thus in 

 trotting horses older sires or dams which have undergone con- 

 siderable training have been supposed to transmit some of the 

 benefits of this training to their offspring. Similarly, acquired 

 knowledge, acquired immunity to disease, etc., have been stated 

 to be transmitted. When these matters are investigated scien- 

 tifically it is found that unintentional selection of parents may 

 account for the bulk of cases. Nor is character of offspring which 

 may be found to be correlated with parental age to be taken as 

 proof of change in germ plasm of parents. Some non-germinal 

 influence may be transmitted. Thus it has been shown (Hart, 

 1923) that Mongolian idiots are at their birth twenty-three times 

 as likely to have mothers forty years of age or over as mothers 

 from twenty to twenty-four. There is no good evidence that 

 Mongolian idiocy is hereditary. 



The material considered in the present paper presents clear 

 evidence of change in average traits of offspring according to age 

 of mothers. Discussion as to whether this difference is germinal 

 will be reserved for a later part of the paper. 



In the parasitic wasp Habrobracon juglandis (Ashmead) which 

 has been bred under constant environmental conditions, ab- 

 normalities in antennae, external genitalia or posterior part of the 

 digestive tract occur. 



Abnormal antennas may be branched, bent or clubbed. 



Gonapophyses of the female (sensory appendages forming 

 sheath for the sting) may be swollen at the end or twisted from 

 25 371 



