REPORT ON ZOOLOGY. J 95 



to the nervous system. Their particular object is to show that 

 in the Crustacea this system exhibits a unity of composition, and 

 that all the different modifications which it presents in different 

 families may be easily referred to one type, these modifications 

 depending simply on a greater or less approximation, and ten- 

 dency towards centralization of the medullary ganglions. In a 

 fourth memoir, read the same year to the Royal Academy of Sci- 

 ences*, they have considered the respiratory organs of these ani- 

 mals, their researches on which head have led them to discover the 

 true method of respiration in those Crustacea which are capable 

 of living for a considerable time out of water. They have as- 

 certained that it is not by any organ analogous to lungs, as was 

 formerly supposed, but by the help of a peculiar structure, ena- 

 bling them to retain the water within the respiratory cavity as in 

 a reservoir, from whence is supplied the necessary moisture for 

 a free exercise of the branchial laminae. In a subsequent me- 

 moir on this subjectf, published in 1830, M. Edwards has ex- 

 pressed an opinion that the respiratory apparatus will be found 

 to afford some valuable characters for the determination of natural 

 groups. 



The above memoirs on the anatomy of the Crustacea, with 

 the exception of the last, were undertaken by MM. Audouin 

 and Edwards jointly. During the present year (1834), M. Ed- 

 wards has published singly the first volume of a general work | 

 gn the natural history of this class, in which he has embodied 

 the researches just alluded to, as well as treated of the classifica- 

 tion and systematic description of these animals. The following 

 is a sketch of his arrangement. He divides the Crustacea pri- 

 marily into the three subclasses of Crustaces Maxilles, Crust. 

 Suceurs, and Crust. Xyphosuriens. The first of these groups 

 conunences with the legion Podophthalmiens, including the two 

 orders Decapodes and Stomapodes ; then follows the legion 

 Edriophthalmes, comprisiiig the three orders Amphipodes, Iso- 

 podes, and Lcemipodes; next in succession are the legions 

 Branchiopodes and Entomostracts, which he thinks form two 

 parallel series, the former containing the two orders of Phyllo- 

 podes and Cladoc^res, the latter those of Ostrapodes and Cope- 

 podes, this last being nearly the same as the order Dicladopes 

 of Latreille. The legion Trilobites is placed provisionally at 

 the end of the first subclass. The second subclass is divided 



• A report by Cuvier and Dumeril on this memoir will be found in the Ann. 

 des Sci. l^at., torn. xv. p. 85. 



t Ann. des Set., torn. xix. p. 451. 



J Histoire Naturelle des Crustaces, comprenant V Anatomie, la Physiologic, et, 

 la Classification de ces Animanx, par Milne Edwards, torn, i., Paris, 1834. 



o2 



