Chap. XXVII. OF PANGENESIS. 371 



Before proceeding to show, firstly, liow far these assump- 

 tions are in themselves probable, and secondly, how far they 

 connect and explain the various groups of facts with which 

 we are concerned, it may be useful to give an illustration, as 

 simple as possible, of the hypothesis. If one of the Protozoa be 

 formed, as it appears under the microscope, of a small mass of 

 homogeneous gelatinous matter, a minute particle or gemmule 

 thrown off from any part and nourished under favourable 

 circumstances would reproduce the whole ; but if the upper 

 and lower surfaces were to differ in texture from each other 

 and from the central portion, then all three parts would have 

 to throw off gemmules, which when aggregated by mutual 

 affinity would form either buds or the sexual elements, and 

 would ultimately be developed into a similar organism. 

 Precisely the same view may be extended to one of the 

 higher animals ; although in this case many thousand 

 gemmules must be thrown off from the various parts of the 

 body at each stage of development; these gemmules being 

 developed in union with pre-existing nascent cells in due 

 order of succession. 



Physiologists maintain, as we have seen, that each unit of 

 the body, though to a large extent dependent on others, is 

 likewise to a certain extent independent or autonomous, and 

 has the power of increasing by self-division. I go one step 

 further, and assume that each unit casts off free gemmules 

 which are dispersed throughout the system, and are capable 

 under proper conditions of being developed into similar units. 

 Nor can this assumption be considered as gratuitous and 

 improbable. It is manifest that the sexual elements and buds 

 include formative matter of some kind, capable of develop- 

 ment ; and we now know from the production of graft-hybrids 

 that similar matter is dispersed throughout the tissues of 



p. 441) shows how different they Lastly, it appears from a review of 



really are. I formerly thought that the present work by Prof. Mante- 



the "physiological units " of Herbert gazza (' Xuova Antologia, Mag2;io,' 



Spencer (' Principles of Biology,' vol. 1868), that he (in his ' Elementi di 



i., chaps, iv. and viii., 1863-64) Igiene,' Ediz. iii., p. 540) clearly 



were the same as my gemmules, but foresaw the doctrine of pangenesis. 

 I now know that this is not the case. 



