12 On the present state of Zoology. 
the Crustacea appear, according to the views of this naturalist pub- 
lished some years back, is identical with the genus Zoea of Bosc : the 
second is here affirmed to be the genus Megalopa of Dr Leach. The 
species in which this double metamorphosis has been more particular- 
ly noticed is the Carcinus Mosnas.* We have said that doubts exist 
respecting the accuracy of these observations. It is rather singular 
that in the same volume in which Mr Thompson's paper is contain- 
ed, there should be also one by Mr Westwood, who is opposed to the 
views of that gentleman, and who, in our opinion, has very much 
shaken the grounds for believing in the existence of any metamor- 
phosis at all. Mr Westwood has not only shown that Mr Thomp- 
son's statements are too vague and indefinite, and his observations too 
deficient in details, to be accepted as conclusive of this question, but 
he has brought forward some observations of his own of a directly 
contrary nature. From specimens of the female of the West Indian 
land crab, he has obtained both eggs and young, some of the latter 
being evidently just hatched ; and he finds these young, as well as 
the embryo in the egg, bearing the exact form of the adult animal. 
It may further be added that Mr Westwood has found the young of 
the common crab of a much smaller size than Mr Thompson's sup- 
posed full-grown Zoea which died on the point of undergoing its sup- 
posed metamorphosis.f 
In reviewing the memoirs which have appeared of late years in il- 
lustration of the structure of animals, there is yet another circum- 
stance which merits our attention ; and that is the endeavour to elu- 
cidate the affinities even of those belonging to the higher classes, by 
having recourse to anatomical investigation. The importance of this 
step in the case of the Mollusca, and of other tribes occupying a low 
place in the scale of organization, has been already alluded to, and 
for some time been duly appreciated by naturalists. But, compara- 
tively speaking, it is only more recently that such researches have 
been extended to the vertebrate and annulose animals, with an ex- 
press view to the object above-mentioned. To enter into any detail- 
ed analysis, or even to particularize the titles of the different memoirs 
which have appeared of this character, would lead us beyond the li- 
mits to which we must necessarily restrict this article. But we wish 
* On the supposed existence of Metamorphosis in the Crustacea Phil. Trans. 
1835, p. 311. 
f Zool. Research, p. 9 It may not be out of place to mention here for the 
information of our own naturalists, that the supposed Metamorphosis of the 
Crustacea has been recently proposed as the subject of a prize -essay by the 
Academy of Sciences at Haarlem See L'Institut, 1835, p. 272. 
