340 COELENTERATA — ANTHOZOA chap. 



few exceptions Alcyonaria show no signs of having been torn, 

 bitten, or wounded by carnivorous animals. It is improbable 

 that the presence of nematocysts in the tentacles can account for 

 this immunity, as it is known that some predaceous animals do 

 feed upon Coelenterates provided with much larger nematocysts 

 than any Alcyonarian possesses. All Alcyonaria, however, have 

 a characteristic disagreeable odour, and it is possible, as in many 

 other cases, that this is accompanied by an unpleasant taste. 

 But if the Alcyonaria themselves are immune, it is possible that 

 their large yolk -laden eggs may form a not unimportant source 

 of food supply. In places where large colonies flourish, an 

 immense number of eggs or embryos must be discharged into the 

 water during the spawning season, and of these only a minute 

 fraction can survive long enough to found a new colony. 



Reproduction. — The formation of colonies by gemmation has 

 frequently been mentioned above. The young buds of a colony 

 arise from the endoderm canals in the body-wall of the zooids, in 

 the general coenenchym, or in the stolon. They never arise 

 from evagination of the coelenteric cavities of the zooids. There 

 is no evidence that fission of a colony to form secondary colonies 

 ever occurs. G-emmation leads to the increase in the number 

 of zooids forming a colony, but not to an increase in the number 

 of colonies. 



Fission of the zooids is of extremely rare occurrence ; a single 

 case, however, has been recorded by Studer in the genus Gersemia. 

 Sexual reproduction usually occurs once in a year ; it is doubtful 

 whether it ever occurs continuously. The colonies appear to be 

 nearly always dioecious, only one case of hermaphroditism having 

 yet been recorded.^ The ova and sperm sacs are usually formed and 

 matured on the six ventral mesenteries, rarely on the dorsal pair 

 of mesenteries (Fig. 148, B) as well. The spawning season varies 

 with the locality. Alcyonium digitatum spawns at Plymouth at 

 the end of December, and somewhat later at Port Erin. The 

 Pennatulid Benilla and the Gorgonid Leptogorgia spawn in the 

 summer months on the coast of North America. In the Mediter- 

 ranean Alcyonium palmatum spawns in September and October 

 (Lo Bianco), Go7'gonia cavoUnii in May and June. 



■' OoralUum nobile appears to be the exception to this rule, as it is stated that 

 colonies and even individual zooids are occasionally hermaphrodite. Lacaze 

 Duthiers, "Hist. Nat. du Corail," 1864, p. 127. 



