CLASS OF CBTJSTACEA. 



425 



spoken. Thus the limnadise are enclosed between two oval 

 bucklers, united together after the manner of the valves of the 

 oyster ; and it is after having removed this moveable cuirass, 

 that the true annulated structure of their bodies is observed 

 (Fig. 433) ; the cypris, abounding in stagnant waters, pre- 

 sents an analogous disposition, only the rings of which their 

 bodies are composed are still more difficult to be recognised. 

 Finally, we may cite the lernsea, which at the adult age 

 presents the strangest forms (Fig. 132, 133), but which 



Fig. 420. The Crab (Maia). 



when young has a distinctly annulated structure ( 366). 

 This comparative study of the tegumentary skeleton of the 

 Crustacea presents a great interest, in respect of physiolo- 

 gical anatomy, of which one of the most important branches 

 is to investigate the modifications which nature causes the 

 same organic elements to undergo, to adapt them to various 

 uses, and to create with analogous or homologous materials 

 dissimilar instruments ; but the limits we have assigned to 

 these lectures do not admit of our touching at greater length 

 on this subject. 



[The question here mooted by my friend Mr. Edwards, em- 



