CRUSTACEA. 189 



intestine is finally, with the heart, walled in by the confluence of 

 the lateral lobes of the integument along the middle line of the back. 



The integument is very soft when the animal quits the shell : 

 it subsists, at first, on the remaining portion of the yolk, during 

 which time its coat becomes sufficiently hardened to admit of its 

 moving about in quest of food with more safety. The different ap- 

 pendages increase in length, and more especially the branchiae, the 

 growth of which is now remarkably rapid. The changes of the in- 

 terior parts of the animal, with the exception of the development of the 

 sexual organs, consist in a gradual adaptation of parts already formed 

 to their j^roper functions. 



The relative positions of embryo and vitellus are the same in the 

 craw-fish as in the Daphne pulex and Branchipus stagnalis. The 

 maxillae present at an early period a considerable resemblance to 

 those of the Apus : the legs at the period w^hen they are devoid of 

 branchial ajDpendages typify the persistent condition of the Branch- 

 iopoda : after the branchiae are developed, but before they are 

 enclosed in the branchial chamber, the characteristic persistent con- 

 dition of the respiratory system of the Edriophthalma and Stoma 

 poda is sketched out. M. M. Audouin and Milne Edwards have 

 shown that the successive changes of development of the nervous 

 system of the craw-fish correspond in like manner with distinct types 

 of formation observed by them in its permanent condition in lower 

 species of the class ; thus the double series of ganglions, which first 

 indicate the subcesophageal central part of the nervous system in the 

 embryo craw-fish, is analogous to the permanent state of the nervous 

 system in the mature Talitrus. At a more advanced period the two 

 series of ganglions in the foetal craw-fish approach the median line and 

 become united together as in the abdominal ganglionic chain in the 

 adult Cymothoa. We have seen that in the brachyurous Crustacea 

 a further concentration takes place by the longitudinal blending 

 together of the whole series of the suboeosophageal ganglia, which 

 clearly indicates that the brachyurous Crustacea are more highly 

 developed than the macrourous species ; contrary, however, to the 

 opinion of Dr. Rathke. 



It is certain that the moult of the young craw-fish is not at any 

 period accompanied by a marked change in the form of the body, or 

 in the structure and functions of the locomotive members ; this Crus- 

 tacean, in short, undergoes no metamorphosis. 



A series of less complete observations on the ova of a species of 

 land crab {Gecarcinus)^ more recently published by Mr. Westwood, 

 lead to the same inference in respect of that species. This ac- 

 complished entomologist coincides with Dr. Rathke in the general 



