Apparent Instances and Objections 163 



into another, giving rise to a dorsal groove the mechanical 

 production of which is evident since it undoubtedly re- 

 sults from the pressure of the preceding spiral upon the 

 succeeding. Now in a still more recent geological period 

 paleontological discoveries show that the descendants of 

 these cephalopods with a tightly rolled up shell have begun 

 to unroll, and have then the form of an Archimedes, 

 spiral with broader turns which no longer touch one 

 another. But the dorsal groove persists even in these half 

 rolled up shells, a proof that the younger cephalopods 

 have repeated hereditarily this character which was 

 acquired by their ancestors. 130 



This is certainly a most interesting example, but it 

 has not quite the force of complete proof. For besides 

 the objection, which we shall examine later, that the 

 groove is formed in the non-living substance of the shell, 

 it does not exclude the interpretation, though it be only 

 verbal and without any real foundation, that it was not 

 the rolling up of the spiral upon itself that produced the 

 inherited groove, but rather that both the tight rolling 

 up and the groove were selected and fixed independently 

 of one another by natural selection. 



The influence of dry, hot climates upon the develop- 

 ment of the horns of cattle and sheep is well known. If 

 certain individuals of a certain breed of cattle are trans- 

 ported from a wet, cold climate to a hot dry climate, the 

 horns increase in length and circumference and the skin 

 thickens. The following fact seems to prove that this 

 acquired elongation of the horns is inheritable. A cow r 

 was transported from Algau in Bavaria where the climate 

 is moist and cold, into the dryer and hotter steppes of 



180 Le Dantec : Traite de Biologic. P. 296297. 



