388 



CEUSTACEA. 



Limuius Polyphemus. 



savages it becomes a dreadful weapon, and is used to point their spears 

 either for the chase or war. 



(993.) The reader will at once Fig. 197. 



perceive the strict parallelism that 

 may be traced between the changes 

 which occur during the metamor- 

 phoses of Insects, and those observable 

 as we thus advance from the lowest 

 to the most highly organized Crus- 

 tacean genera; and even the steps 

 whereby we pass from the Annelidan 

 to the Myriapod, and from thence to 

 the Insect, the Scorpion, and the 

 Spider, seem to be repeated, as we 

 thus review the progressive develop- 

 ment of the class before us. 



(994.) Having thus found that the 

 annuli, or rings, which compose the 

 annulose skeleton may be detected 

 even in the most compactly formed 

 Crustacea, it remains for us to in- 

 quire, in the next place, what are the 

 principal modifications observable in 

 the articulated appendages developed from the individual segments. 

 This inquiry is one of considerable interest, inasmuch as it goes to prove 

 that, however dissimilar in outward form, or even in function, the limbs 

 of Crustaceans are mere developments of the same elements, which, as 

 they remain in a rudimentary condition or assume larger dimensions, 

 become converted into instruments of sensation, legs, jaws, or fins, as 



the circumstances of 



, Fig. 198. 



the case may render 



needful. In the lower, 

 or more completely an- 

 nulose forms (figs. 195 

 and 198), these mem- 

 bers are pretty equally 

 developed from all the 

 segments of the body, 

 and are subservient to 

 locomotion, being ge- . 



nerally terminated by prehensile hooks, or provided with fin- like ex- 

 pansions; but as we advance to the more perfect genera, the limbs 

 assume such various appearances, and become convertible to so many 

 distinct uses, that they are scarcely to be recognized as consisting of 

 similar elements modified only in their forms and relative proportions. 



