Protandry and Senescence in Corals. 467 



extraneous, environmental causes, the polyp tissues ceasing to 

 exercise an efficient, protective influence over the outer parts of 

 the epitheca, consequent on its greater thickness. 



With increase of size, beyond 25 mm. in length, the ova ripen. 

 Ducts are formed through the thickened nutritive endoderm down 

 to the ova, which subsequently escape through them. In sections 

 along their lengths they show longitudinal striation, but they are 

 very distinctly ducts. They correspond in fact to the structures 

 termed "cone nutritif " and " Fadenapparut " in Actiniaria, which 

 I would suggest are simply oviducts. 



As the ova ripen they escape, but the place of each of the 

 original ones (2 to 4) is taken by 2 to 4 fresh ova. The several 

 organs on the primary mesenteries of a polyp, whose calicle is 

 about 32 mm. long, form ovoid masses of 6 to 9 closely adpressed 

 ova. A general increase in size of the separate organs takes 

 place, but this, after the ripe testes have once been formed, is 

 never proportional to the general increase in size of the polyps. 

 An ovary with 2 or 3 ova occupies about the same space as a ripe 

 testis, and the increase is only when it comes to consist of 6 or 

 more ova. The area of the nutritive endoderm increases still 

 less than that of the ovary, so that in the largest polyps it covers 

 the generative masses to a proportionably less degree. 



The largest specimen — of the type variety from the Maldives — 

 I have examined was 40 mm. in length. A large number of the 

 ova had escaped, many of the mesenteries having none. On most 

 there were a number of ova, quite isolated from one another. On 

 none of the mesenteries could I find any small ova to take the 

 place of the escaped eggs. Indeed it seemed obvious that a 

 critical period had been reached, after which ova cease to de- 

 velope. No change was at this stage visible in the ectoderm, 

 neither external nor of the mesenterial filaments. The whole 

 endoderm was on the other hand devoid of fat and much vacuo- 

 lated, even the nutritive part over the ovaries being but little 

 granular. A second specimen 36 mm. long from the Cape and 

 a third 33 mm. from the Maldives exhibited like conditions to the 

 larger form mentioned above. 



So far I have referred only to the larger or primary mesen- 

 teries, i.e. those which fuse with the stomodoeum. The smaller 

 mesenteries are always of the same sex as the larger, and appear 

 to exhibit the same changes. Their ovaries do not usually consist 

 each of more than 3 or 4 ova. 



There is no direct proof — indeed it is only a presumption — 

 that the polyp now dies. The annual (?) lines of growth are so 

 regular, right up to whatever size the corallite may be, that 

 obviously growth must be a very orderly process. The largest 

 specimen among over 600 corallites was a Cape of Good Hope 



VOL. XI. PT. VI. 33 



