182 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. Tomy 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. 
