ADULT COLONY. . 37 



In many corals the endoderm in the lower regions becomes thickened to such 

 a degree as to occupy the entire interseptal loculi, but in S. radians a narrow 

 space remains as far as the aboral termination. 



GONADS. 



Among all the polyps which have been examined anatomically ova only 

 have been found to occur. The polyps studied were taken from colonies 

 other than those which extruded larvae. The gonads are situated below the 

 stomodseal region, only one ripe ovum as a rule being present on each mesentery 

 (plate 7, fig. 43). They occur about the middle of the transverse length of 

 the mesentery, and are found on the members of both first and second orders. 

 The ova are usually longer in diameter along the radial axis, and are indented 

 where the septal granules have intruded upon the narrow interseptal chambers. 

 Along with the single large egg may be two or three developing ova without 

 yolk, but the conditions are not favorable for studying their origin from the 

 ordinary endodermal epithelial cells. 



The absence of male sexual elements from the examples studied can by no 

 means be taken as indicating a dioecious character of the species. Wherever 

 thus far in West Indian corals sexual differentiation is suggested the gonads 

 have been found to be female, but where the ova are best developed spermaria 

 have been found to accompany them ; spermaria have never been found alone 

 in any polyp. Hence there is much which suggests that coral polyps are pro- 

 togynous. Mr. Stanley Gardiner, however, has recently discussed the subject 

 of protandry in corals (Proc. Camb. Phil. Soc., XI, 1902). From an investi- 

 gation of a large number of developmental stages in Flabellum rubrum he has 

 been able to show that in this form spermaria arise first on the mesenteries and 

 that ova appear later, when the production of sperm acini ceases. " The ova 

 grow enormously, with the final result that the mass becomes entirely female, 

 consisting of usually 2 or 3 large ova, flattened on their sides against one another 

 and occupying the whole area of the former testes." Protandry is thus clearly 

 established in Flabellum rubrum. The claim for protogyny in the West Indian 

 corals hitherto studied rests upon the fact that spermaria have never been 

 found alone, but always in association with large numbers of ova; on the 

 other hand, many polyps have been found with ova alone, often few in number, 

 as if sexual maturity were but beginning. 



Were a general protandry to be assumed, we should have to suppose 

 that all the polyps containing only ova had passed beyond their male 

 period and extruded all their spermatozoa, becoming wholly female. Prob- 

 ably, as in other groups of animals and plants, no hard and fast rule is 



