AND THE LOWER ANIMALS. 29 



as it were plunged in a nourishing hath, and conse- 

 quently a heart and blood-vessels ; in fact, a system of 

 irrigation, is not at all required. Their presence or 

 absence is merely indicative of a higher or lower 

 organization. Hence it follows that the young and 

 adults of many species do not possess a vascular 

 system. 



All the systems of organs whose order of succession 

 we have been considering are connected with the 

 preservation of the individual. Those connected 

 with procreation, and which ensure the perpetuation 

 of the species, appear at a much later date than any 

 of the others. We must bear this general law in 

 mind, for not only is it applicable to all animals 

 which undergo transformations, but in those subject 

 to metamorphoses and geneagenesis it is even still more 

 marked. 



The various apparatus we have mentioned are all 

 complex enough, being each composed of several 

 organs, and these again being built up of different 

 tissues. Hence we naturally inquire how three folds 

 of such a simple character as those of the germinal 

 area, have been able to give rise to such a complicated 

 machinery, and under what form the material which 

 the vital force has thus transformed, appears in the 

 beginning. Before going further, then, we must con- 

 sider a few fundamental laws, and analyze a theory 

 whose name at least is familiar to all anatomists. 



All naturalists who have investigated this subject 

 agree in stating that every organ consists in its ear- 

 there mixing with the products of secretion and digestion, consti- 

 tutes a fluid to which the term ' nourishing bath] employed in the 

 text, seems hardly inappropriate." 



