252 Analt/tical 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 developenient of Insects 

 we know at present scarcely any thing. From a comparison 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 Vertehrata, 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 

 antennae, 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 



