44 
GUIDE TO THE COEAL GALLEEY. 
Case 3. 
tentacles at the base and scattered knobbed tentacles above. The 
two kinds of tentacles can be clearly seen in this specimen with the 
aid of a simple lens. 
Hy dr actinia echinata * (Figs. 8, 9) is always found forming a white 
fleecy covering on univalve shells inhabited by Hermit Crabs. “ The 
waving forest of tall and graceful polypites generally reaches its 
greatest height towards the mouth (of the shell), round the edge of 
which are set the curious snake- 
like appendages. Intermingling 
with the perfect polypites are the 
rudimentary zooids, which carry 
the generative sacs, attenuated by 
their work and looking as if 
weighed down by their burden” 
(Hincks). The polyps rise from a 
chitinous crust covered with conical 
serrated spines. 
Monocaulus imperator * (Fig. 
10), one of the most remarkable 
acquisitions of the Challenger Expe- 
dition, was obtained from depths 
of 1,875 and 2,900 fathoms in 
the North Pacific. A naked stem 
over seven feet in length, and 
bulbous at the lower end, is sur- 
mounted by a large polyp with 
basal and oral circles of filiform 
tentacles. The polyp was pale 
pink, and measured nine inches in 
breadth across the expanded basal 
circle of tentacles. The exhibited 
specimen (Case 3) is sadly altered 
from what it was in life ; but, as 
Sir Wyville Thompson observed, 
“these delicate things, drawn up rapidly through the water from a 
depth of four statute miles, suffer greatly from this violent change.” 
The specimens almost seemed to melt away, and had to be 
promptly put into alcohol, which has hardened and contracted them 
to their present condition. 
Cordylophora lacustris* is a fresh-water Hydroid, with branches 
rising from a creeping stolon to a height of two or three inches ; 
Fig. 5. 
a. Diagram of a Hydroid feeding polyp 
(longitudinal section) ; b, of a Hy- 
droid Medusa, o, mouth ; gr, gastric 
cavity ; t, tentacle ; si, structureless 
lamella ; g', jelly between ectoderm 
and endoderm ; rh, radial canal ; 
v , velum ; rik, circular canal. (From 
Lang’s Text-book Comp. Anat.) 
