On the present state of Zoology. 1 
ly so called, are sufficiently great to mislead the inexperienced naturalist. 
Equally important are those changes which have been traced with so 
much attention and care by Duges in the case of the Acari,* and 
which have thus accounted for the apparent anomaly of hexapod and 
octopod forms coexisting in the same group. But there are other 
classes in which the metamorphosis is more complete, and attended 
by such an entire alteration of habits and economy, that by no pos- 
sible a priori reasoning could we have been led to consider the young 
and adult states of such animals, if seen separately, as pertaining to 
the same species. Who would have suspected that the sluggish Bar- 
nacle, imnaoveably fixed to some rock or other marine substance, had 
ever enjoyed a free independent existence, swimming rapidly in the 
sea under the form of a small bivalve crustacean ? Still less who 
would have anticipated the nature of those changes which attend the 
early development of the compound Awidioe ? animals appearing at 
birth as separate individuals, and endued with the power of locomo- 
tion, uniting afterwards to form one common inert mass ! Yet these 
are the striking discoveries which have been made known of late years 
by different observers, and the accuracy of which there appears no 
reasonable ground for doubting. Now it will hardly be questioned 
whether it be important for the naturalist to be acquainted' with 
these changes occurring in certain animals. It is obvious that, except 
he be, he will be constantly mistaking the immature states of such 
animals for distinct species, or perhaps be even referring them to dis- 
tinct genera. We know that such errors in fact have occurred over 
and over again. Thus the larvae of the Acari were, until the re- 
searches of Duges, regarded as permanent forms, and made to consti- 
tute a peculiar family in that group comprising several genera. The 
same was the case formerly with some of the Entomostraca. It is 
also probable that many of the minute animals, which now stand in 
our systems as distinct forms, are only the first states of some of the 
higher ones, in which the existence of metamorphosis remains to be 
discovered.-)- But it is not merely to avoid the overmultiplication of 
genera and species that this acquaintance with animals at different 
periods of their growth is wanted. It is necessary in order to obtain 
correct views respecting their affinities. There was a time when, to 
attain this object, it was thought sufficient to look only to the per- 
fect state of the species, and scarcely any notice was taken of the 
* Ann. des Sci. Nat. 1834, torn. i. pp. 5 and 144; and torn. ii. p. 18. 
f Milne- Edwards thinks it probable that some of the Cercarice are only the 
young of the compound Ascidice during the first stage of their existence. Sec 
Lamarck's Hist. Nat. des An. sans Vert. (2d edit.) torn. i. p 428. 
