the term Homology in modern Zoology. 35 
logue “the same organ in different animals under every 
variety of form and function ;” by analogue, “ a part or organ 
in one animal which has the same function as another part or 
organ in a different animal.” But how can the sameness (if 
we may use the word) of an organ under every variety of 
form and function be established or investigated? This is, 
and always has been, the stumbling-block in the study of 
homologies without the light of evolutionism; for, to settle 
this question of sameness, an ideal “ type” roup of 
organisms under study had to be evolved from the human 
mind, after study of the component members of the group ; 
and then it could be asserted that organs might be said to be 
the “same” in two animals which had a common representa- 
tive in the ideal type. i4 
This reference to an ideal type was the only criterion o 
homology ; and yet we find those who have adopted the doc- 
trine of evolution making use of the term “ homology” with- 
out any explanation. The study of homologies was brought 
under a very important influence from the appreciation of the 
value of developmental changes in indicating the similarities 
tury so much advanced science) would understand by homo- 
d 
not consistently have the same meaning as a Platonist; and 
yet it appears that, from the force of habit or some accidenta 
cause, the term homology és used at the present time in the 
old sense by many authors who accept the doctrine of evolu- 
tion, or at any rate not with any definite meaning which has 
been agreed upon by those who belong to the new school. 
Without particularizing the authors whose views are alluded 
to, we may mention the attempt to trace the homologies of the 
bones of the skull in detail through the vertebrate series, the 
y of the chain of nerve-ganglia of Arthropoda with 
the sympathetic of Vertebrata, the homology of the four cavi- 
ties of the heart and also of the individual muscles of the 
limbs in Sauropsida and Mammalia, and especial the so- 
called serial homologies of the fore and hind limbs in Vertebrata 
and of the teeth of the upper and lower jaws. is 
