118 J. MATTHEWS ON THE HISTORY AND 



water. As the water in the lower part of the great sponge-like 

 coral mass rises and falls with the tides, so will the water near the 

 surface : and this will keep fresh, if the mass be sufficiently com- 

 pact to prevent much mechanical admixture ; "but where the land 

 consists of great loose blocks of coral with open interstices, if a well 

 be dug, the water, as I have seen, is brackish " (Darwin.) 



With this, Mr. Chairman and Gentlemen, I now conclude, earn- 

 nestly assuring you that I have been speaking as a student to 

 students, and that the best fate that I can wish for this paper is 

 that it may arouse discussion, and perhaps excite criticism. In either 

 case I shall be content, for my purpose will have been answered. 



Note. — I have been requested to append a few words on the relation of the 

 microscope to Corals. I may therefore say that on every point they are 

 essentially microscopic, their masses, though so great, extensive, and widely 

 spread, being composed, for the most part, of microscopic units. Of course, 

 the polypes cannot be examined in this latitude except by the light which 

 their British congeners throw on them. But their hard structures can be 

 instructively examined — 1st. By horizontal sections cut by the usual 

 methods employed for very hard tissues. 2nd. By a plan communicated to 

 me by Mr. Stewart, viz., splitting them vertically by the sharp blow of a 

 hammer upon a razor; or 3rd. By splitting them by means of a pair of cut- 

 ting pliers, such as are used for wire. By either of these last methods, the 

 most interesting and beautiful structure is revealed, which is also so delicate 

 that it would be quite destroyed and lost by grinding, and can be properly 



examined by the Microscope only. 



J. M. 



EXPLANATION OF PLATE VIII. 



Fig. 1. — Transverse section of a Hydrozdon, showing the body-cavity in 

 the form of a single tube, enclosed by the body-walls. 



Fig. 2. — Transverse section of an Actinozoon .- s, Digestive sac; m, One of 

 the primary mesenteries dividing the body-cavity into vertical 

 compartments. Between the six primary mesenteries are seen 

 the secondary and tertiary mesenteries, which fall short of the 

 walls of the stomach, a, Ectoderm ; b, Endoderm. 



Fig. 3. — Diagrammatic vertical section of a Sea-Anemone : a, Mouth ; s, 

 Stomach; b, Body-cavity ; cc, Convoluted cords ("craspeda') 

 containing thread-cells, and forming the free edges of the 

 mesentery (m) ; tt, Tentacles ; o, Reproductive organ contained 

 within the mesentery. The Ectoderm (e) is indicated by the 

 broad external line, the Endoderm (e 1 ) by the thin line and the 

 space between that and the Ectoderm. 



Fig. 4. — Actinia rosea (after Gosse). 



Fig. 5. — Calicular gemmation as seen in Lonsdaleia jioriformis. Car- 

 boniferous. 



