252 Analytical Notices of Books. 
by other writers, and points out the coincidences and discrepancies that 
occur between them. Cavolini, Jurine, Prevost and Herold are the only 
authours who have treated of this difficult subject ; the first in a very 
superficial manner, in a memoir on the Generation of Fishes, &c., MM. 
Jurine and Prevost in several valuable papers on the structure and de- 
velopement of different species of Branchiopoda, and M. Herold in his 
laborious work on Spiders. Of the primitive developement of Insects 
we know at present scarcely any thing. From acomparison of his results 
with those of M. Herold, Dr. Rathke concludes that there exists a 
close resemblance between the structure and developement of the Crawfish 
and of Spiders, and consequently a near relation between the types of 
their organization. The most important particular in which they agree is 
in the relative position of the vitellus, which lies in both at the back of 
the embryo, instead of being placed, as in the Vertebrata, in front. A 
remarkable difference between the two is, however, found in the develope- 
ment of the abdomen, which in the Spider is applied from the very com- 
mencement to the surface of the vitellus, while in the Crawfish it makes its 
appearance in the shape of a perfectly free appendage. The same relative 
position of embryo and vitellus, and many minor points of coincidence, 
are met with in Daphnia Pulex according to Jurine, and in Branchipus 
stagnalis according to Prevost. In the latter the abdomen is highly deve- 
loped, and occupies the same position with respect to the embryo as in the 
Spiders. The authour also derives some convincing proofs of the jus- 
tice of M. Savigny’s hypothesis above noticed from the developement of 
the trophi and legs of the Cyclops 4-cornis as described by Jurine. 
Under his third head, the authour’s first object is to prove that the 
Crawfish and its congeners are among the most highly organized of the 
long-tailed Crustacea, each of their external organs being as fully deve- 
loped as the corresponding part in any other macrourous species, and the 
whole of them taken together appearing to occupy a middle station in 
size, as compared to each other, with reference to a similar comparison 
carried through the rest of the tribe. Proofs of this are adduced in 
the forcipated terminations of the legs, the bipartition of the posterior 
antenne, the spurious legs beneath the tail, the laminated appendages of 
the last named organ, and the consistence and completeness of the outer 
covering. In the second place he combats Lamarck’s opinion that the 
