Rathke, Growth of the Eggs of the Crawfish. 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 opposed 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 antenne are shorter, smaller, and less developed; the bran- 
chiz 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 Squille in this particular, as well as in its legs being apparently de- 
rived from the tail. Its maxille have at one period a considerable likeness 
to those of Monoculus Apus. Its legs and their branchial appendages 
resemble those of certain Branchiopoda. Jt 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 connecting 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 inthe adult Tulitrus, which occupies a very 
