Rathke, Growth of the Eggs of the Cratvfixh. 253 



Brachyourous Crustacea are more highly developed than the Macrourous, 

 and maintains that however strongly one or two particulars in the organi- 

 zation of the former may argue in favour of this supposition, the weight of 

 evidence is decidedly ojjposed to it. Thus, for example, the trunk of 

 the Brachyura retains the same comparative breadth after its complete 

 developement as that of the Macroura in the early part of its foetal state ; 

 the tail of the former is not only less developed as a whole, but also less 

 perfect in its parts ; the anterior pair of legs alone are furnished with double 

 claws ; the antennae are shorter, smaller, and less developed ; the bran- 

 chiae are less numerous and more simple; the two ventral nervous cords 

 do not approach to a union with each other in the posterior half of the 

 trunk, but remain at a distance, &c. &c. Lastly he points out analogical 

 relations between the Crawfish in its various stages of developement, and 

 the lower Crustacea in their permanent state. Thus at an early stage of 

 its growth, when its articulations are indistinctly marked, it resembles 

 the SquillcE in this particular, as well as in its legs being apparently de- 

 rived from the tail. Its maxillae have at one period a considerable likeness 

 to those of Monoculus Apus. Its legs and their branchial appendages 

 resemble those of certain Branchiopoda. It wants the spurious legs, 

 which are developed only at a late period, and thus resembles many 

 of the lower Crustacea, which never possess them, &c. &c. This part 

 of the subject, however, is treated by the authour in too superficial a 

 manner, with reference to the importance of the questions which it in- 

 volves; and is by no means so happily illustrated as might have been 

 expected.* 



• Since the above paragraph was written, MM. Audouin and Milne Edwards 

 have published, in the Annales des Sciences Naturelles for June of the present 

 year, a note on the Nervous System of the Crustacea, which fully justifies our 

 last observation. Referring to Dr. Rathke's Work, and coiinecting his disco- 

 veries with their own previous researches Into the structure of Crustacea, they 

 show that the three successive stages of developement in the nervous system 

 of the Crawfish exactly correspond with three apparently distinct types of 

 formation observed by them in its permanent condition in other animals of the 

 Class. Thus, the double series of ganglions, under the form of which the 

 thoracic nerve first makes its appearance in the ovum of the Crawfish, is perfectly 

 analogous to its permanent state in the adnit Ta/itru-i, which occupies a very 



