EVIDENCE FROM EMBRYOLOGY 73 



has jointed appendages, nervous, muscular and 

 digestive systems and, in short, clearly belongs to 

 that group of the Crustacea which includes the 

 barnacles. This is degeneration carried nearly to 

 the utmost possible extreme and yet the individual 

 development shows the derivation of this otherwise 

 problematical parasite and the steps through which 

 it passed in its deterioration. 



It was stated above that several distinguished nat- 

 uralists altogether reject the recapitulation theory as 

 a means of interpreting the facts of embryology. 

 They do this on the ground that, inasmuch as changes 

 and innovations in form or structure must arise in the 

 germ-plasm, at the very beginning of ontogeny, 

 there is no reason why such changes might not in- 

 volve the whole course of embryological develop- 

 ment. To my mind this d priori objection to the 

 recapitulation theory is quite without force in view 

 of the great body of observed facts, but there is no 

 time to enter upon a discussion of such an abstruse 

 and difficult problem. For our present purpose, 

 however, it is important to note that these objectors 

 are staunch evolutionists and find in the community 

 of mode in ontogeny between different classes of 

 organisms one of the strongest arguments in support 

 of the evolutionary doctrine. 



Here may be conveniently considered the very in- 

 teresting and significant blood tests which have 

 been made in the last fifteen years by various physi- 

 ologists and especially by Dr. George H. F. Nuttall, 



