THE ANIMAL-PLANTS, 137 
four perfectly different systems of organs; by the intestines, 
the vascular system, the organs of respiration, and the 
urinary apparatus. In Zoophytes, however, these functions 
and their organs are not yet separate, and are all performed 
by a single system of alimentary canals, by the so-called 
gastro-vascular system, or the ccelenteric apparatus of the 
intestinal cavity. The mouth, which is also the anus, leads 
into a stomach, into which the other cavities of the body also 
open. In Zoophytes the body-cavity, or “cceloma,” possessed 
by the four higher tribes of animals is still completely 
wanting, likewise the vascular system and blood, as also the 
organs of respiration, ete. 
All Zoophytes live in water; most of them in the sea, only 
a very few in fresh water, such as fresh-water sponges 
(Spongilla) and some primeval polyps (Hydra, Cordylo- 
phora). A specimen of the pretty flower-like forms which 
are met with in great variety among Zoophytes is given on 
Plate VII. (Compare its explanation in the Appendix.) 
The tribe of animal-plants, or Zoophytes, is divided into 
two distinct provinces, the Sponges, or Spongie, and the Sea- 
nettles, or Acalephe (p. 144). The latter are much richer 
in forms and more highly organized than the former. In all 
Sponges the entire body, as well as the individual organs, 
are differentiated and perfected to a much less extent than 
in Sea-netiles. All Sponges lack the characteristic nettle- 
organs which all Sea-nettles possess. 
The common primary form of all Zoophytes must be 
looked for in the Protascus, an animal form long since 
extinct, but whose existence is proved according to the 
biogenetic principle by the Ascula. This Ascula is an 
ontogenetical development form which, in Sponges as well 
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