EMBRYOLOGY AND CLASSIFICATION. 303 
life with characters peculiar to Radiates, and 
ends it without assuming any feature of a higher 
type. The Mollusk starts with a character es- 
sentially its own, in no way related to the Ra- 
diates, and never shows the least tendency to 
deviate from it, either in the direction of the 
Articulate or the Vertebrate types. This is 
equally true of the Articulates. At no stage of 
growth are their young homologous to those of 
Mollusks or Radiates any more than to those of 
Vertebrates, and in their final development they 
stand equally isolated from all others. That this 
is emphatically true of the Vertebrates has already 
been fully recognized ; and the facts known with 
reference to this highest type of the Animal King- 
dom might have served as a warning against the 
loose statements still current concerning the so- 
called infusorial condition of the young Inver- 
tebrates. These results are of the highest impor- 
tance at this moment, when men of authority in 
science are attempting to renew the theory of a 
general transmutation of all animals of the higher 
types out of the lower ones. If such views are 
ever to deserve serious consideration, and be ac- 
knowledged as involving a scientific principle, it 
will only be when their supporters shall have 
shown that the fundamental plans of structure 
characteristic of the primary groups of the Ani- 
mal Kingdom are transmutable, or pass into one 
