FUNDAMENTAL RELATIONS OF ANIMALS 55 



among Crustacea, the Cancroidea or the Pinnotheroidse, the Limu- 

 loidas or the Cypridoidse, and the Rotifera;'^- among Worms, the 

 Dorsibranchiata or the Naioidas; among Molkisks, the Stromboidas 

 or the Buccinoidas, the Helicinoidas or the Limnasoida?, the Chama- 

 cea or the Cycladoidas; among Radiata, the Asterioidas and the Ophi- 

 uroidas, the Hydroids and the Discophorae, the Astraeoidas and the 

 Actinioidae. 



Having thus recalled some facts which go to show what are the 

 limits within which size and structure are more directly connected,'^^ 

 it is natural to infer, that since size is such an important character 

 of species, and extends distinctly its cycle of relationship to the fami- 

 lies or even further, it can as little be supposed to be determined by 

 physical agents as the structure itself with which it is so closely con- 

 nected, both bearing similar relations to these agents. 



Life is regulated by a quantitative element in the structure of all 

 organized beings, which is as fixed and as precisely determined as 

 every other feature depending more upon the quality of the organs 

 or their parts. This shows the more distinctly the presence of a spe- 

 cific, immaterial principle in each kind of animals and plants. All 

 begin their existence in the condition of ovules of a microscopic size, 

 exhibiting in all a wonderful similarity of structure. And yet these 

 primitive ovules, so identical at first in their physical constitution, 

 never produce anything different from the parents; all reach respec- 

 tively, through a succession of unvarying changes, the same final re- 

 sult, the reproduction of a new being identical with the parents. How 

 does it then happen that, if physical agents have such a powerful in- 

 fluence in shaping the character of organized beings, we see no trace 

 of it in the innumerable instances in which these ovules are dis- 

 charged into the elements in which they undergo their further de- 



"Dana, Crustacea, pp. 1409, 1411. 



■^^ These remarks about the average size of animals in relation to their structure 

 cannot fail to meet with some objections, as it is well known that under certain cir- 

 cumstances man may modify the normal size of a variety of plants and of domesticated 

 animals, and that even in their natural state occasional instances of extraordinary 

 sizes occur. But this neither modifies the characteristic average, nor is it a case which 

 has the least bearing upon the question of origin or even the maintenance of any 

 species, but only upon individuals, respecting which more will be found in Sect. xvi. 

 Moreover, it should not be overlooked that there are limits to these variations and 

 that though animals and plants may be placed under influences conducive to a more 

 or less voluminous growth, yet it is chiefly under the agency of man that such changes 

 reach their extremes. (See also Sect, xv.) 



