302 TlMEHRl. 
and amount of budding or branching where this deve- 
lopment takes place. The term " Zoophytes" is thus 
the popular designation of the group of animals which, 
from their simple bag-like cavity, are technically known 
as the Coelentera or Hollow-entrailled animals. 
Considerable modifications of this plan, however, take 
place among different members of the group, and tend to 
hide the structural simplicity of their organisation. 
Among the sponges, the grasping organs are absent from 
the mouth, stinging cells are never developed, and the 
walls or sides of the body become so perforated that the 
colony forms a variably shaped porous mass : among the 
coral class, the lower part of the bag becomes divided 
up by vertical partitions where usually a calcareous 
deposit — coral — is formed ; while in the jelly-fishes, the 
body as a rule is vastly swollen out by gelatinous matter, 
and the bag-like structure is thereby almost obliterated. 
In the greater number of forms, a third or middle layer 
of cells, developed from the outer layer of the body, 
is clearly indicated, and in the sponges especially, 
becomes markedly abundant. Nerves and muscular 
fibres developed from this layer, and thus primarily 
derived from the portion of the body in contact with the 
outer world, are here met with in their simplest condi- 
tion, and present themselves as isolated and scattered 
patches or threads, very unlike the cord-like and band- 
like tissues of the higher animals. No rudiments of a 
distinct circulatory system exist in any of these 
organisms, but the nutrient fluid elaborated by the inner 
cell-layer, passes throughout the whole body from cell to 
cell. In the colony-building forms, however, as the 
various parts are organically connected by the stem-like 
