TRANSACTIONS OF SECTION D. 621 



the minnows. The question, then, is, whether fish reared for some generations 

 under conditions which compelled them to adopt habits not conformable to their 

 natures would show any corresponding change of instinct. Of course each genera- 

 tion would be reared in a separate tank from its parents. Moths — Experiments 

 liave been made for the author by Mr. Frederic Merritield with the Selenia Ulus- 

 traria, which has two broods yearly. They are being made for quite another 

 purpose, but have already shown the ease of breeding hardy moths on a large 

 scale when the art of doing so is well understood. All larvae are fastidious in 

 their diet, bat it may well be that certain food which they would not touch at 

 first would after a while be greedily eaten, and be found perfectly wholesome. 



Experiments on the lines here suggested ought to show the proportion of cases 

 in which acquired aptitudes of several kinds are certainly not inherited. They 

 might also, perhaps, show that in a small proportion of cases they certainly are. 

 Thus limits would be fixed within which doubt remained permissible. The object 

 of this paper is to invite experts to discuss the details of the most appropriate 

 experiments for doing this. 



2. The Palceontological Evidence for the Transmission of Acquired Characters. 

 By Professor Henry F. Osborn. * 



As a contribution to the present discussion upon the inheritance of acquired 

 characters I ofl'er an outline of the opinions prevailing among American naturalists 

 of the so-called Neo-Lamarckian school, and especially desire to direct attention to 

 the character of the evidence for these opinions. This evidence is of a diflerent 

 order from that discussed in Weismann's essays upon * Heredity,' and while it 

 cannot be said to conclusively demonstrate the truth of the Lamarckian principle, 

 it certainly admits of no other interpretation at present, and lends the support of 

 direct observation to some of the weightiest theoretical difficulties in the pure 

 Selection principle. 



1. We regard natural selection as a universal principle, explaining the 

 'survival of the fittest' individuals and natural groups, and as the only explana- 

 tion which can be offered of the origin of one large class of u.seful and adaptive 

 characters. "We supplement this by the Lamarckian principle as explaining the 

 ' origin of the fittest ' in so far as fitness includes those race variations which 

 •correspond to the modifications in the individual springing from internal reactions 

 to the influences of environment. There is naturally a diversity of opinion as to 

 how far each of these principles is operative, not that they conflict, 



2. If both principles operate upon the origin of the fittest we should find 

 in every individual two classes of variation, both in respect to new characters and 

 to modifications of the old : First, chance variations, or those which, with Darwin 

 and Weismann, we attribute to the mixture of two diverse hereditary strains; 

 these may or may not be useful ; if useful they depend entirely upon selection for 

 their preservation. Second, variations which follow from their incipient stages a 

 certain definite direction toivards adaptation ; these are not useful at the start ; thus 

 while, as they accumulate, they favour the individual, they are not directly 

 vlependent upon selection for theii' preservation ; these we attribute to the 

 Lamarckian principle. 



My present purpose is to show that variations of the second class are of an 

 extent and importance not suspected previous to our recent palceontological 

 discoveries, and that the Lamarckian principle oflers the only adequate explanation 

 for them. 



3. The general theory as to the introduction and transmission of variations of 

 the second class may be stated as based upon the data of paleontology — the 

 evolution of the skeleton and teeth. 



(1) In the life of the individual, adaptation is increased by local and general 

 metatrophic changes, of necessity correlated, which take place most rapidly in the 

 regions of least perfect adaptation, since here the reactions are greatest. (2) The 

 main trend of variation is determined not by the transmission of the full adaptive 

 modifications themselves, as Lamarck supposed, but of the disposition to adaptive 



