132 ESSAY ON CLASSIFICATION. 



course of their development. 1 The snug berth in which 

 the young of all Mammalia undergo their first transforma- 

 tion the womb of their mother, excludes so completely 

 the immediate influence of any external agent, that it is 

 only necessary to allude to it to show how independent 

 their growth must be of the circumstances in which even 

 the mother may be placed. This is equally true of all 

 other vivaparous animals, as certain snakes, certain sharks, 

 and the viviparous fishes. Again, the uniformity of tem- 

 perature in the nests of birds, and the exclusion, to a cer- 

 tain degree, of influences which might otherwise reach 

 them, in the various structures which animals build for 

 the protection of their young or of their eggs, 2 show dis- 

 tinctly, that the instinct of all animals leads them to re- 

 move their progeny from the influence of physical agen- 

 cies, or to make these agents subservient to their purposes, 

 as in the case of the ostrich. Reptiles and terrestrial 

 Mollusks bury their eggs to remove them from varying 

 influences ; fishes deposit them in localities where they 

 are exposed to the least changes. Insects secure theirs in 

 various ways. Most marine animals living in extreme 

 climates lay their eggs in winter, when the variations of 

 external influences are reduced to a minimum. Every- 

 where we find evidence that the phenomena of life, though 

 manifested in the midst of all the most diversified phy- 

 sical influences, are rendered independent of them to the 

 utmost degree, by a variety of contrivances prepared by 

 the animals themselves for self-protection, or for the pro- 

 tection of their progeny from any influence of physical 

 agents not desired by them, or not subservient to their 

 own ends. 



1 Biscnopp (Tn. L. W.), in R. 2 BURDACH'S Physiologic, etc., q. 



Wagner's Handworterbuch der Phy- a. 2d ed. vol. 2, Sect. 334-8. See, also, 



siologie, Article " Eutwickelungs- KIBBY and SPENCE'S Introduction, 



geschichte," p. 885. etc., q. a. 



