OF PLANORBIS AT STEINHEIM. 101 



" That the variations of the sculpture, as also those of the other characteristics of the 

 shells of Ammonites first make themselves visible upon the last (outer) volution, then 

 such a variation advances in the following generations step by step always nearer to the 

 beginning of the spiral, until it covers the greater part of the (inner) whorls." 



The difference between our statements^ is that Wiirtenberger speaks of the inner 

 whorls and I use the word "young" in place of the word "inner whorls," because the 

 inner whorls of all shells represent the first formed or younger stages of growth. 



I also in the first quotation use a phrase " entirely passing over " which has been 

 included in parentheses because it refers to the skipping of characteristics in development, 

 a phase of the law of quicker inheritance, or acceleration in heredity, which Herr Wiirten- 

 berger also mentions, but which is not included in his first statement. I might also refer 

 if I chose to similar quotations from Prof E. D. Cope of Philadelphia, showing that he, 

 simultaneously with me, discovered the same law though giving it a somewhat different 

 application than either Wiirtenberger or myself 



Now we have only to understand, that the outer whorls are built during the full grown 

 or adult period, and the inner by the animal during the younger stages, in order to per- 

 ceive that this is a statement that the Ammonites inherited the adult characteristics of 

 their ancestral forms at earlier and earlier periods in successive generations. 



This is the law of acceleration, and it is specifically given by Herr Wiirtenberger in 

 various places in his book, notably on p. 98, where he attributes the preservation of any 

 characteristic differences which may arise, to natural selection, and says that they may be 

 inherited earlier or later in the life of individual descendants. 



Then as the earlier inheritance of these characteristics would, be of advantage to the 

 individual in the struggle for existence, Herr Wiirtenberger thinks that successive gener- 

 ations would tend to inherit them at earlier and earlier periods. The objections to this 

 seemingly simple and straightforward explanation are numerous. Animals do not inherit 

 the new characteristics which their parents may have acquired at later periods than those 

 in which they appeared in the parent, but at the same time, or earlier in the immediate 

 descendants, and eventually always earlier in the more remote descendants. I have as yet 

 seen no evidence that the descendants inherit a characteristic at a later period than that 

 •at which it first appeared in an adult ancestor. 



Even if this assumption should be proven it would still remain necessary to establish the 

 nature of the characteristics inherited, whether they really were advantageous or not. 



Nothing can exceed the confidence with which the strict Darwinist assumes, without 

 any appeal to observation, that all characteristics which are inherited are necessarily 

 advantageous. Exactly the reverse is very often true. The disadvantageous, the 

 advantageous, the parallelisms and the differences, are all subject to the law of acceler- 



'In order to see how closely we have followed the same the later existhig individuals, until finally many character- 

 path it is also necessary to compare the statements on pages istics altogether disappear." " Cephalopods of the Mus- 

 27 and 28 of this Memoir, and in the following essays: " De- eum: Embryology." Bull. Mus. Comp. Zool., Cambridge, 

 velopment of the shells of Ammonoids and Nautiloids." Mass., Vol. 3, No. 5, p. 70-71. " Evolution of the Arietidae." 

 Proc. Bost. Soc. Nat. History, Vol. 14, p. 398. "This is Proc. Bost. Soc. Nat. Hist., Vol. 17, p. 238. "Genetic 

 the law of acceleration, or the perpetual reduction of adult relations of Stephanoceras," in same, Vol. 18, p. 379, last 

 characteristics to earlier and earlier periods in the growth of paragraph, p. 382. 



