226 THE VOYAGE OF H.M.S. CHALLENGER. 



C. Style of one of the dactylozooids, seen in section. 



B. Large canals of the ccenosarc, occurring in the pseudosepta or intervals 



between the dactylopores. 

 S. Surface layer of the ectoderm. The main mass of tissue is composed 

 of the finer ramifications of the coenosarcal meshwork. 

 Fig. 13. Small portion of the coenosarcal meshwork of Sporadopora dichotoma, greatly 

 magnified in order to show the histological structure ; as seen in osmic acid 

 preparations. 



C. Channel of the canal. 

 Ed, En. Endoderm layer. 

 M M. Membranous layer. 

 E E. Ectoderm. 



T. Nematocysts in process of development. 

 Fig. 14. Two pigmented cells of the endoderm of the same, highly magnified. 



PLATE XII. 



Shows the structure of the ccenostea of several species of Stylasteridre. 



Fio-s. 1-4. Stenohelia profunda. Off St Thomas, Danish West Indies. 450 fathoms. 



Fi°s. 1,2. Specimens drawn of the natural size to show the mode of branching. 



Fig. 3. A specimen enlarged to show the arrangement of the cyclo-systems. a Two eyclo- 

 systems of the same, to show the mode in which the young terminal cyclo- 

 systems bud out from the adult axial systems, and the arrangement of the 

 ampulke around one of the latter. 



Fig. 4. Diagrammatic longitudinal section through two calicles such as shown in the 

 foregoing figure. At the base of the tube of the young cyclo-system is seen 

 the minute style. The anipullge are laid open. 



Figs. 5, G. Conopora tenuis. Off the Kermadec Islands. 650 fathoms. 



Fig. 5. A specimen drawn of the natural size, a The same enlarged. The stem is 

 deformed, being enlarged, and hollowed out by a cavity occupied in the recent 

 state by a parasitic Annelid, b Mouth of one of the cyclo-systems much 

 enlarged. 



Fig. 6. Diagrammatic longitudinal section through one of the cyclo-systems to show its 

 two chambers, the form of the gastropore and its connections with the 

 dactylopores. 



Fig. 7. Oryptohelia pitdica. Lat. 25° 45' N., long. 20° 12' W. 1525 fathoms. 



