136 THE HISTORY OF CREATION, 
(vegetative or gastral) mass. Whether there still exist _ 
representatives of this group is uncertam. Their former 
existence is undoubtedly proved by the two exceedingly 
important ontogenetic animal forms which we have already 
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 
Planeada and Gastreada. The type of the Planeada is 
the Planwa—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 Gastrwada is the Gastrewa, 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 
Gastrea, 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 Caleareous 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 
