178 THE DOCTRINE OF DESCENT. 



adaptation. It gives rise to the remarkable poly- 

 morphism, which appears especially in the marvellous 

 forms of the Hydra tuba; and, higher up, iri the 

 organization of the communities of the Termites and 

 the Bee, &c. 



So far as modification coincides with adaptation, the 

 direct adaptations hitherto discussed may be contrasted 

 with a series of indirect adaptations. Among these may 

 be comprised a series of phenomena of which the causes 

 do not fall within the life of the individual, but are to 

 be sought in influences by which the parents were af- 

 fected. It is obvious that we here come into contact with 

 the province of heredity, which is well known to breeders. 

 Thus H. V. Nathusius, in his studies on the formation 

 of the pig's skuU,"^ says: — "From the facts here col- 

 lected, it is plain that the transmission, the transfer of 

 the form of head from the parents to the offspring, does 

 not unconditionally ensue. If the form of skull, which 

 we will briefly term the cultivated form, be the product 

 of nutrition and mode of life, hence of external influ- 

 ence, — if it can be differently formed in the same indi- 

 vidual, and is therefore not constant, — in that case the 

 heredity of this form cannot be spoken of without quali- 

 fication. The form itself will not be transmitted to the 

 offspring, but only the tendency to the form. This may 

 be inferred from the circumstance that from generation 

 to generation, and to a certain degree, the form increases 

 in peculiarity. If we rear a common with a thorough- 

 bred pig, and if we allow exactly the same influences 

 of nutriment and keeping to operate upon both, and in 

 equal measure, we shall not obtain the same form of 

 head. The development of the form of head must there- 



