REPORT ON CORALS—EXPLANATION OF PLATES. 227 
Fig. 7. A large finely-grown specimen, but with one principal branch broken off. a Side 
view of one of the cyclo-systems and its attached branches, to show the 
form of its margin and of its lid. _b Two cyclo-systems of the same viewed 
from above, to show the form and extent of the lids. 
Fig. 8. Distichopora trregularis. Off Samboangan, Philippine Islands. 10 fathoms. 
Fig. 8. A specimen of twice the natural size to show the distribution of the lines of 
pores. a Tip of a branch of the same, much magnified to show the arrange- 
ment of the gastropores and dactylopores. 
PLATE XIII. 
All the figures except fig. 7 represent structures occurring in Millepora nodosa. 
. 1, Ovoid nematocyst, confined in position to the bases of the zooids and general 
om 
superficial layer, not occurring in the tentacles. «@ The cell expanded. 
b The cell with the thread fully projected. The respective lengths of the 
various parts of the thread and cell are drawn exactly according to measure- 
ments. 
Fie. 2. Three-barbed nematocyst, of the form peculiar to Hydrozoa, occurring in the 
tentacles of the zooids and also sparingly on the general surface of the coral. 
a The cell with its head protruded and thread partially projected. 6 The cell 
in the unexpanded condition. The figures are drawn exactly to measurements. 
Fig. 3. View of a portion of the ccenosteum, magnified 2 diameters. 
Fie. 4. View of the surface of the ccenosteum, magnified 80 diameters, showing one com- 
plete system of pores, composed of a central gastropore, and eight surrounding 
smaller dactylopores. 
Diameter of the central gastropore = 0°25 mm. 
Largest diameter of the whole group of pores = 1°5 mm. 
Drawn by Dr J. J. Wild, Artist to the Challenger Expedition. 
Fig. 5. Enlarged view of a vertical section of the ccenosteum, 
C. Zooid-cavity or pore. 
B, B. Branches of the canal-system, 
Fig. 6. Section of the coenosteum cut parallel to its outer surface, showing a portion of 
a system of zooids. 
C. Gastropore in horizontal section. 
C’, C’. Dactylopores. 
B’. Branch of a canal-system which communicates hy means of a lateral 
offset with one of the dactylopore cavities. 
