172 M. Agassiz on the Relations between Animals 



the younger state of the pupa, and the pupa the younger state of 

 the perfect Insect. But in the same ratio as we find so frequently 

 throughout the animal kingdom that the lower condition of struc- 

 ture and development of a type is manifested in a more bulky 

 body, so we find among Insects, that their earlier state of meta- 

 morphosis which is developed under inferior circumstances, 

 reaches its final growth in a more bulky body than that of fol- 

 lowing periods during which their successive moultings and the 

 transformations of the substance of the body take place ; the 

 greatest size which the larva acquires is first reduced in its trans- 

 ition into a chrysalis, and this again is reduced in its transition 

 into a pei'fect insect, — the development of wings only leaving 

 them seemingly of greater size when their surface is extended, 

 though the bulk as a whole be reduced. Weighing these animals 

 in these different states of development will satisfy the most incre- 

 dulous of the reality of what is here stated, should the appearance 

 have deceived him before. A Silkworm when it begins to spin 

 is much heavier than the chrysalis, and this heavier than the per- 

 fect Moth. Without directly weighing these animals, we might 

 be satisfied about this fact if we consider the amount of silk 

 which is thrown out by the latter, and the amount of fluid 

 which is discharged by the Moth even before it rids itself of its 

 load of eggs and sperm to enjoy the last moments of its complete 

 maturity. 



If we now allude to the Vertebrata we shall find very similar 

 facts, and perhaps in the animals to be mentioned, inducements 

 for the discovery of curious unnoticed connections. And here 

 again we should be cautious, for reasons alluded to already above, 

 not to take the classes as such, but rather to consider their dif- 

 ferent types separately ; for the class of Fishes as a whole cannot 

 be said to contain the largest Vertebrates, nor even to afford any 

 support to the view that aquatic animals in general are larger than 

 terrestrial, for we find proportionably a much greater number of 

 large species among Mammalia than among Fishes } we find a 

 greater number of large terrestrial Reptiles than of aquatic ones. 

 But if we review the classes separately, and consider their secon- 

 dary groups by themselves, we find that the rule holds good, but 

 bears, at the same time, most interesting reference to the order 

 of succession in geological times, as the respective types of any 

 given group are the larger in the present period, whether terrestrial 

 or aquatic, for being representatives of families which had nume- 

 rous representatives in older periods. Among Fishes, we find the 

 largest in the family of Sharks and Skates, Sturgeons and Gar- 

 pikes, the first of which are exclusively marine, the second ma- 

 rine and fluviatile, the third entirely fluviatile ; but the three 

 types are either exclusively representatives of families largely 



