No. 517] 



PARENTAL MODIFICATIONS 



17 



Even this possibility can not be dismissed without a 

 hearing. 



5. The offspring themselves, during their fetal life, 

 may have been influenced in some way by the differences 

 of temperature to which the mothers were subjected dur- 

 ing the first two weeks of pregnancy (see above). It is 

 obvious, however, that in a warm-blooded animal, the 

 fetus could not be directly affected by differences of tem- 

 perature as such. It would be curious, indeed, if the 

 parental modifications should be so closely paralleled 

 under these circumstances. 



6. The germ-cells of the parents may have been so 

 affected by the external conditions to which the latter 

 were subjected that modifications resulted in the off- 

 spring similar to those which were produced in the par- 

 ents directly. This hypothesis has been invoked again 

 and again to account for a certain class of facts which 

 would seem at first sight to lend strong support to the 

 Lamarckian hypothesis, e. g., by Weismann and by Tower. 

 Such an explanation could not, however, be applied in the 

 present case without, radical modification. For we may 

 again point out that in a warm-blooded animal differences 

 of temperature, as such, could not affect either the fetus 

 or the germ-cells to any appreciable extent. 16 The sug- 

 gestion might be made, however, that the effects of tem- 

 perature, even upon the parent body itself, may not be 

 direct, but may be due to the formation of specific chem- 

 ical substances which, through the medium of the blood, 

 may be supposed to simultaneously influence the body 

 and the germ-cells. Such a hypothesis can neither be 

 proved Jior disproved in the present state of our knowl- 

 edge, but it is perhaps the type of explanation which is 

 calculated to appeal most strongly to the biologist of 

 to-day. It may be pointed out, however, that if a mech- 



