THE VEGETABLE AND ANIMAL KINGDOMS. 135 



the crab and lobster did not make their appearance till 

 the Triassic epoch. The Cirripede is a high articulate animal, 

 and the sessile cirripede is superior to . the pedunculated, 

 "the sessile being apparently the perfection of this line of 

 being." The embryo cirripede passes through a distinctly 

 entomostracau form. We should therefore expect that the 



FIG. 77. 





Metamorphoses of Crab. 



A, first stage ; B, second stage ; C, third stage, in which it begins to 

 assume the adult form ; D, perfect form. 



cirripedes should appear after the entomostraca, and the sessile 

 after the pedunculated. It is so. The cirripedes do not enter 

 upon the stage till the Oolitic era ; and, while the peduncu- 

 lated first appear in the Stonesfield slate, and are conspicuous 

 in the chalk, the sessile are not seen till the tertiary. The 

 Insects pass through a distinct metamorphosis, being, at an 

 early period of their foetal existence, essentially annelidans or 

 worms. In the geological record, annelidan forms occur in 

 the Silurian age, the full insect not till the carboniferous. 

 One great section of the insects go through a more perfect 

 metamorphosis than the other, having at one time the form of 

 an inactive pupa which takes no nourishment, but passes 

 through many, though gradual, changes. Now it is exceed- 

 ingly curious that, while the insects of least perfect metamor- 

 phosis (Ametabold) are first detected in the carboniferous age, 

 and become prominent in the Jurassic, those of most perfect 

 metamorphosis (Metabola) did not enter on the scene till 

 afterwards. Agassiz likens the Ametabola to the cryptogamia, 

 and the Metabola to flowering plants, and adds that " it is 

 well worthy of remark that among plants the cryptogamic, 



