On the Brain in Vertebrates and Invertebrates. 303 
distinct faunistic factors seem to have played a part. The 
North-American element is represented by two, no doubt 
artificially introduced, species of white ants, and certain large 
dragon-flies, which having flown over at some time continue 
to breed. The Australian element is very small, and proba- 
bly consists solely of thesingle ant-lion, which may be regarded 
as Polynesian. The strictly endemic element is the largest, 
and is represented by (dnter alia) the Agrionide and the 
peculiar forms of Chrysopide, two groups of very different 
habits—the former necessitating a constant supply of fresh 
water with aquatic animal life for food, the latter a supply of 
small soft-bodied plant-frequenting insects on which their 
larvee feed. 
Such, then, is my opinion on the materials for the order of 
insects of which I have made a special study ; but any broad 
generalization on the Insect-fauna must be left until the 
reports of other specialists on the results of Mr. Blackburn’s 
investigations can be collated and correlated. 
XXXIV.—On the Answerable Divisions of the Brain in Ver- 
tebrates and Invertebrates. By Prof. Owen, C.B., F.R.S., 
&e. 
THE principles or generalizations of homology and analogy 
force themselves on the attention of naturalists in many 
relations, and suggest questions on divers subjects. ‘Take the 
heart of a Cephalopod, for example. Is it the homologue or 
the analogue of that of a fish? Is its relation thereto 
only that of identity of function, sometimes expressed by the 
term “ homodynamous,” which is synonymous with “ ana- 
logous ” in questions of this nature ? 
No naturalist, it may be presumed, doubts the homology as 
well as analogy or homodynamy of the heart of the cuttle-fish 
with the heart of the snail. If the latter were propounded as 
the subject of the inquiry, a biologist of eminence might pro- 
nounce that it was merely homodynamous with the heart of a 
fish, conceiving relations of position to be essential in deter- 
mining the question of homology. Accepting the current 
views of such topical relations he might, probably would, 
reply, “‘ The heart of the snail is on the back or ‘ dorsal’ aspect 
of the body, while that of the fish is on the opposite or ‘ ven- 
tral’ aspect.” 
22* 
