136 THE HISTORY OF CREATION. 



(vegetative or gastral) mass. Whether there still exist 

 representatives of this group is uncertain. Their former 

 existence is undoubtedly proved by the two exceedingly 

 important ontogenetic animal forms which we have ah-eady 

 described as Planula and Gastrula, and which still occur as a 

 transient stage of development in the ontogeny of the most 

 different tribes of animals. Corresponding to these, we may, 

 according to the biogenetic principle, assume the former 

 existence of two distinct classes of Blastularia, namely, the 

 Planceada and Gastrceada. The type of the Planceada is 

 the Plancea — long since extinct — but whose historical por- 

 trait is still presented to us at the present day in the widely 

 distributed ciliated larva (Planula). (Frontispiece, Fig. 4.) 

 The type of the Gastrceada is the Gastrcea, of whose 

 original nature the mouth-and-stomach larva (Gastrula), 

 which recurs in the most different animal tribes, still gives 

 a faithful representation. (Frontispiece Fig. 5, 6.) Out of the 

 Gastrsea, as we have previously mentioned, there were at 

 one time developed two different primary forms, the Pro- 

 tascus and Prothelmis ; the former must be looked upon as 

 the primary form of the Zoophytes, the latter as the primary 

 form of Worms. (Compare the enunciation of this hypothesis 

 in my Monograph of the Calcareous Sponges, vol. i. p. 464.) 



The Animal-plants (Zoophyta, or Coelenterata) which con- 

 stitute the second tribe of the animal kingdom, rise con- 

 siderably above the primitive animals in the characters of 

 their whole organisation, while they remain far below most 

 of the higher animals. For in the latter (with the excep- 

 tion only of the lowest forms) the four distinct functions of 

 nutrition — namely, digestion, circulation of the blood, 

 respiration, and excretion, — are universally accomplished by 



