118 Mr. St. George Mivart on the Use 
birds and mammals) it may be replied that it is a complex 
correspondence between parts as to their relative positions, 
according to a certain line of thought, and independently of 
their mode of origin; in other words, conformity to type. 
'This answer will, Í know, be distasteful to some; but I con- 
tend that it is a very rational answer for all that. It is true 
that types have none but an ideal existence, that types, as 
types, are not real, objective entities ; but that is no more rea- 
son for refusing to recognize their ideal existence and their 
objective realization in individuals than is the non-existence 
objectively of species, as species, a reason for refusing to re- 
cognize their individual realization or to make use of zoologi- 
cal specific names. 
An intellect of a higher order than that of man would pro- 
bably detect an indefinite number of relations between two 
animals between their component parts, which relations 
escape us altogether. As it is, we can detect a certain num- 
ber of relations of function, of origin, and of conformity of 
relative position of different kinds according to the different 
ways in which we regard the subject matter, 7. e. as we follow 
up different lines of thought. It is well to have distinct 
names for at least the more obviously different conceptions 
of this kind, about a quarter of a hundred of which may be 
readily distinguished. 
r. Lankester proposes to use the word “ homotrophy”’ to 
denote that kind of homoplasy which is due to causes at work 
other and “ besides an agreement in environment or external 
evoking conditions." 
I would suggest the term “ actinology " to denote that kind 
of homological relation which exists between the successive 
segments, regions, or divisions of a part or organ. Processes 
or parts annexed to or springing from such segments, regions, 
or divisions would be secondarily actinologous, while appen- 
dages of these latter again would be tertiary actinologues, and 
80 on. 
In this way we may have :— 
_1. Non-homologous analogues, 4. e. parts which have a 
similarity of function without any similarity as to relative 
position, e. g. the legs of a lizard and those of a lobster. 
- Homologous analogues, 7. e. parts which are similar both 
as to function and relative position, e.g. the wings of a bat 
and a bird 
3. Homogenetie homologues, 4. e. parts which, on the evo- 
lutionary theory, have a genetic relation, e.g. the humerus of 
a horse and that of an ox. 
4. Developmental homogens, 7. e. homogenetie homologues 
