l82 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



mere bag, without appendages, muscles, nervous system, sensory 

 apparatus, digestive tract, or any determinable organs save those of 

 reproduction. The creature has the power of assimilating the nutri- 

 tive juices which are conveyed to it by the root-like filaments from the 

 body of its host, and the power of reproduction, and it must have some 

 respiratory and excretory capacity, though there are neither gills nor 

 glands. From an examination of the adult parasite alone, it would be 

 quite impossible to classify it and determine the type and class to 

 which it should be referred, but embryology solves the problem. From 

 the egg is hatched a free-swimming larva, which has jointed append- 

 ages, 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 naturalists alto- 

 gether 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 involve the whole course of embryological develop- 

 ment. To my mind this a 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 abstract 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 organ- 

 isms one of the strongest arguments in support of the evolutionary 

 doctrine. 



