142 THE HISTORY OF CREATION. 



of three different classes, namely, the Hood-jellies (Hydro- 

 medusse), the Comb-jellies (Ctenophora), and the Corals 

 (Coralla). The hypothetical, extinct Archydra must be 

 looked upon as the common primary form of the whole 

 group ; it has left two near relations in the still living 

 fresh-water polyps (Hydra and Cordylophora). The 

 Archydra was very closely related to the simplest forms 

 of Spongiae (Archispongia and Olynthus), and probably 

 differed from them only by possessing nettle organs, and 

 by the absence of cutaneous pores. Out of the Archydra 

 there first developed the different Hydroid polyps, some 

 of which became the primary forms of Corals, others the 

 primary forms of Hydromedusse. The Ctenophora de- 

 veloped later out of a branch of the latter. 



The Sea-nettles differ from the Spongise (with which 

 they agree in the characteristic formation of the system of 

 the alimentary canal) principally by the constant posses- 

 sion of nettle organs. These are small bladders filled with 

 poison, large numbers — generally millions — of which are 

 dispersed over the skin of the sea nettles, and which burst 

 and empty their contents when touched. Small animals 

 are killed by this ; in larger animals this nettle poison 

 causes a slight inflammation of the skin, just as does the 

 poison of our common nettles. Any one who has often 

 bathed in the sea, will probably have at times come in con- 

 tact with large Hood-jellies (Jelly-fish), and become ac- 

 quainted with the unpleasant burning feeling which their 

 nettle organs can produce. The poison in the splendid blue 

 Jelly-fish, Physalia, or Portuguese Man-of-war, acts so 

 powerfully that it may lead to the death of a human being. 



The class of Corals (Coralla) lives exclusively in the sea, 



