27 
losing it being over, all the former caution and gentleness are laid 
aside, it is pulled to the polype’s mouth with a surprising violence.” 
I think as much time as can be spared has now been given to 
the notice of the tentacles, so we will pass on; we next see that 
the outline of the gastric cavity and its extension into tentacles is 
dark owing to the presence of chlorophyll corpuscles which are 
contained in the endoderm cells. The ectoderm being transparent, 
as before stated, gives the light outer border to the parts. At the 
end of the animal opposite to the mouth is the pedal disc, the ecto- 
derm cells of which secrete a clear tenacious fluid, emit pseudo- 
podia by which the animal slowly moves (Pseudopodia are the 
blunt processes protruded by low forms of life for purposes of loco- 
motion). 
N ae examine the ectoderm more closely ; we saw before that 
it forms the outer layer of the body wall. It consists of—(1) 
Covering cells, the surfaces of which are exposed along the body 
ahd base irregularly, the latter reaching to the supporting lamina. 
(2) Epithelial muscle cells, the surface of which is exposed; the 
base forming the muscular filament, and is applied to the support- 
ing lamina. (8) Interstitial cells, which are small irregular’ 
masses between the base of (1) 2.e., the covering cells. (4) Young 
enidoblasts which are deeply placed. (5) Fully formed cnidcblasts 
which are superficial. In the cnidoblast the nemalocyst or thread 
-cell is developed, the parent cell persisting as a capsule surrounding 
it, and is produced at its outer or free surface into a small process, 
the cnidocil. (6) Gland cells, these are restricted to the pedal 
disc. (7) Ganglion cells, with numerous outrunners continuous as 
in the endoderm with the cnidoblasts. Sense cells appear to be 
wanting. 
A supporting lamina separates the ectoderm from the endoderm 
éverywhere except at the mouth. It is delicate, containing fila- 
ments for both ecto and endodermal muscle cells. The endodermal 
cells are ciliated, of variable shapes, and during life are amceboid,. 
#.e. changing. Hndodermal cells, so called, which contain chloro- 
phyll corpuscles are vacuolated to a certain extent, the vacuoles in 
some cases being so large as to reduce the protoplasm of the cell to 
a very thin peripheral Jainella These cells throw out pseudopodia 
during digestion and also develop in the walls of the gastric cavity 
_musele filaments which move both circularly and longitudinally. 
Professor Ray Lankester by his Researches on Hydra and 
Spongilla has clearly established the fact that the green bodies of 
these animals have not the value of cells. They are devoid of 
nucleus and membrane. The chlorophyll bodies in Hydra closely 
resemble the corresponding structures in plants, and appear like 
them to multiply by fission. They are at one time entirely absent 
from the ovum, which is the only ectoderm cell that contains them. 
