134 HISTOEY OF CRUSTACEA. Chap. XII. 



in the process of development in tlie higher and lower 

 Crustacea. In the latter all new body- segments and 

 limbs which insert themselves between the two termi- 

 nal regions of the Naiiplius, are formed in uninterrupted 

 sequence from before backwards ; in the former there is 

 further a new formation in the middle of the body (the 

 middle-body), which pushes itself in between the fore- 

 body and the abdomen in the same way, as these have 

 done on their part between the head and tail of the 

 Nauplius. Thus, that which appears probable even 

 from the comparison of the limbs of the adult animal, 

 finds fresh support in the developmental history, namely, 

 that the lower Crustacea, like the Insects, are entirely 

 destitute of the region of the body corresponding to 

 the middle-body of the Malacostraca. It seems pro- 

 bable that the swimming feet of the Copepoda, as also 

 of the pupse of Cirripedia and Khizocephala, represent 

 the abdominal feet of the Malacostraca, that is to say, 

 are derived by inheritance from the same source with 

 them. 



It would be easy to weave together the separate 

 threads furnished by the young forms of the various 

 Crustacea, into a general picture of the primitive his- 

 tory of this class. Such a picture, drawn with a little 

 skill, and finished in lively colours, would certainly 

 be more attractive than the dry discussions which I 

 have tacked on to the developmental history of these 

 animals. But the mode of weaving in the loose threads 

 would still in many cases be arbitrary, and to be 

 effected with equal justice in various ways ; and many 



