RECAPITULATION 57 



demonstrated. It " may be maintained with the same degree 

 of certainty as that with which astronomy asserts that the 

 earth moves round the sun, for a conclusion may be arrived 

 at as safely by other methods as by mathematical calcu- 

 lations." There is no need to appeal to embryology for 

 confirmation. Essentially the problem is one for the thinker, 

 not for the embryologist. If, however, we do appeal to em- 

 bryology we find the evidence exactly such as might have 

 been expected. A history is plainly revealed by every 

 embryo ; but, as I say, it is a history with great inaccuracies, 

 with vast omissions and some additions, both omissions and 

 additions being greatest in the earlier stages. We do not 

 find, nor should we expect to find, in the embryo, in a state 

 of potentially functional perfection, those organs by means 

 of which, at a period immensely remote, lowly types main- 

 tained their existences. Their organs, having lost their 

 functions, have disappeared or are disappearing, or remain 

 merely as foundations on which the functional structures 

 of the foetus and adult are built. Thus in man the vermi- 

 form appendix is disappearing. Thus, also, the branchial 

 arch no longer conveys blood to functional gills; it serves 

 merely as a foundation to the vascular system which is 

 developed later. On the other hand we never find lowly forms 

 swimming about attached to umbilical cords and placentas. 

 These are late additions superimposed on an earlier stage. 



95. Some such theory of development as that outlined 

 above is held by the great majority of biologists. It is a 

 remarkable fact, therefore, that the doctrine of recapitulation 

 is almost completely ignored in every formal theory of 

 heredity that is at all well known. Such theories are 

 usually attempts to explain the facts of development on 

 morphological grounds. The " architecture " and composition 

 of the germ-cell, the derivation and destination of its various 

 " units," are the principal objects of study. Darwin has his 

 gemmules, Spencer his physiological units, Galton his stirps, 

 Haeckel his plasidules, Weismann his biophors, Nageli his 

 micella, De Vries his pangenes. The theory of recapitu- 

 lation, on the other hand, is essentially physiological. It 

 supposes that the germ-cell is of such a " nature," or has such 

 a " function," that under fit conditions it tends to develop by 

 repeating the life-history of the race, thus growing into an 

 organism much like the parent form. No attempt, impossible 

 of verification in the present state of our knowledge, is made 

 to pry into the morphological details of the germ-plasm. 

 The germ-plasm is conceived merely as having certain 



