OF PLANORBIS AT STEINHEIM. 27 



under similar influences in respect to the laws governing the size and genesis of the series, 

 they ought, therefore, to come under the same laws as other forms occurring in other 

 localities. 



(7.) That this appears to be the case except in so far as they are a very limited group, 

 confined to a very limited field, a field free from competition, and extremely favor- 

 able to their growth for that and other reasons. 



These conclusions being approximately arrived at our next inquiry is very naturally, 

 what is this law of heredity and growth which maintains the type, causes parallelisms and 

 constrains variation under ordinary conditions, but still, in certain cases, is forced to give 

 way to physical influences. 



Ruling out the lost or transient forms which are not perpetuated we see that the funda- 

 mental law here, as elsewhere, is that all the characteristics are inherited after they are 

 once introduced. 



Our first inquiry, then, must be as to the mode in which they are inherited. Is there 

 any law which embraces this class of phenomena in some general statement ? 



In former essays, especially written for this purpose, I have tried to show that there 

 was such a general law which is so plain and simple that I have wondered that no authors 

 have made it the basis of investigation except Prof Cope and myself. 



In every series of animals which I have studied the same fact appears, namely, that in 

 a given number of generations inherited characteristics of every kind tend to appear in 

 the descendants at earlier stages than that at which they first occurred in the ancestral 

 forms. Whether characteristics are normal or abnormal, provided they are fixed in the 

 race either by the action of natural selection or by the direct working of physical causes, 

 they are inlierited according to this law. 



Though led to this discovery, if it is such, by close observation of small series of 

 Ammonoid forms, I have since applied it, with greater or less success, to every series of 

 animals which have come imder observation, and in fact it is a corollary of the doctrine 

 of evolution. 



The law of Biogenesis which is now quite generally adopted in Europe, though long 

 since used habitually by the students of Prof Agassiz^ in this country, and regarded by 

 them as an essential basis of investigation, leads naturally to a search for some such 

 uniformity in the inheritance of characteristics as that described above. How can 

 an animal in its transient stages of growth resemble the permanent adult characteristics 

 of ancestral forms without the action of some such law ? 



A negation is not proof, though so often regarded in that light, nor is it proof that in 

 some individual cases a disease or characteristic is inherited later in the life of that 

 particular individual. These instances, and they are not very frequent, are exceptions, 

 and this investigation simply shows that the ordinary action of this law, which has been 

 called the law of accelerated development or acceleration by Cope and myself, has been 

 interfered with by the action of external causes. The only proof against it must be of 

 such a character as that upon which it is founded, namely, the investigation and published 

 description of some genetically connected series of closely allied species, which do not 

 develop in accordance with or verify its provisions. 



^ Prof. Agassiz did not give his law an evolutionary called " Hseckel's law" in Europe, 

 application nor a name, Haeckel did both, and it is now 



