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 irregularis. 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. 



Fig. 1. Ovoid nematocyst, confined in position to the bases of the zooids and general 

 superficial layer, not occurring in the tentacles. a 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. 



Fig. 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. b 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. 



Fig. 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 ccenosteum 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 by means of a lateral 

 offset with one of the dactylopore cavities. 



