212 RAMBLES AND REVERIES. 



54, 57, 58, 59, and 60, will show that the resemblance 

 is maintained through succeeding stages up to the 

 adult condition. 



Crustacean metamorphosis has of late years been 

 a most fascinating study for many naturalists. Just 

 as we have the pupa and chrysalis of insects, so 

 we have various stages in the development of 

 crustaceans, and many members of this class are 

 strikingly alike in their early condition. There is 

 the Nauplius stage, a term derived from the name 

 of one of the lowliest crustaceans, the Zoca or water- 

 flea stage, the Mysis or opossum-shrimp stage, and 

 others. The lobster passes through half-a-dozen of 

 these stages, and the trilobite, according to Barrande, 

 who enjoyed exceptional opportunities for studying 

 it, passed through even more, resembling in its 

 earliest stage the Ostracoda in having no joints to 

 the body. Not that all crustaceans pass through 

 every one of these metamorphic stages, but some go 

 through one and some through another, and thus 

 their place in the zoological tree is determined. 



It is upon these principles that a line of descent 

 has been drawn, which connects the trilobite with 

 the king-crab. The Belinurus, one of the ancient 

 king-crabs, appeared at about the geological time 

 when trilobites were dying out, as has just been 

 observed, while the young of the Limulus, the king- 

 crab of our day, is similar to the adult trilobite ; 

 hence it has come to be a widely received opinion 

 that Limulus has the best right to be considered 

 the descendant and representative of the ancient and 

 noble race of trilobites. 



