502 ON THE STEUCTUEE OF TORITES, 



nematocyst (i. e. about 2 jx), appeared to Lave spiral lines running 

 round it, and, when cut across, I saw it on more tbau one occa- 

 sion hexagonal with the sides inwardly curved. While it is fairly 

 safe to assume that these are defensive weapons *, more extended 

 researches with better preserved, material would be necessary to 

 throw light on their structure and to discover their origin and 

 the nature of their contents and method of discharge. ^ 



The internal tissues were much disorganized (1) by the sym- 

 biotic algae and (2) by the great quantities of slime. The former 

 Avere large, very numerous, and often found dividing. They 

 occurred in greatest numbers in the extendible or projecting parts 

 of the polyp, that is, doubtless, where the light can reach them, 

 although they also occur scattered among the cceoosarcal canals. 



The slime seemed to have filled the internal cavity with a net- 

 work of darkly staining strands, quite different from the bright 

 carmine of the ectoderm-cells of the gullet. 



Among the fragments of the ccenosarc which appear in the 

 sections separated by the clear spaces left by the decalcified 

 skeleton, the interseptal loculi can be made out by their radial 

 arrangement, and by the presence of the mesenterits, which are 

 here correspondingly narrowed. Different conditions would 

 doubtless be found in other forms in which the intrathecal 

 skeleton did not rise to the level of the walls. 



Small as this contribution to the subject is, my work on the 

 sections having been unexpectedly interrupted, it is enough to 

 show the desirability of an extended study of the soft parts of 

 diff'erent species of the genus. 



EXPLANATION OF PLATE 35. 



The six photographs here reproduced are from negatives kindly lent, for the 

 illustration of this paper only, by the Trustees of the Natural History 

 Museum. All are enlarged fiye times. 



Fig. 1. Pontes with full number of pali typically arranged ; the directives 

 point in all directions. 



* At the suggestion of my friend Prof. Howes, I have compared these organs 

 with figures of large cells with thick, coiled threads given by Weymouth 

 Eeid (Phil. Trans. 1894, B) for the skin of the Eel, and Goodrich (Q. J. M. Sci. 

 xxxix.) for the coelomic corpuscle of the Oligochtete EiichytrcBus. As Prof. 

 Howes points out, these latter seem to be curious modifications of ordinary 

 slime secretions. While I can trace only slight structural resemblance between 

 these cells and those described above and Porites, the fact that here again 

 tliey are associated with immense numbers of slime-cells suggests a line of 

 enquiry which might be followed up. 



