408 COELENTERATA ANTHOZOA chap. 



and the directives. The tentacles correspond with the inter- 

 mesenteric chambers. In some genera there is a constriction of 

 the zooid between the pairs of the tentacles on each side of the 

 axial mesenteries and the directive tentacles. This gives them 

 the appearance of a division into three zooids with two tentacles 

 apiece, one with a mouth and two without a mouth ; and as 

 the mouthless parts alone bear the gonads on the single axial 

 mesentery, they have been called the " gastrozooids " and " gono- 

 zooids " respectively. This must not be regarded, however, as a 

 case of true dimorphism, as the cavities of the so-called gastro- 

 zooid and gonozooids are continuous. 



The Antipatharia are widely distributed in nearly all the great 

 seas of the world. Some species are found in shallow water in 

 the tropics, but most of them occur in depths of fifty to five 

 hundred fathoms. The genus Batliypathes is only found at 

 enormous depths ranging from 1070 to 2900 fathoms. Speci- 

 mens of Cirripathes spiralis, Antipathella gracilis, and another 

 species have recently been obtained in deep water off the west 

 coast of Ireland,^ but these are the only Antipatharia known to 

 occur within the British area. 



The very simple structure of the Antipatharia is usually 

 attributed to degeneration. On this view the Antipathidae with 

 only six complete mesenteries are the most modified, whereas 

 the Leiopathidae with twelve mesenteries are more closely related 

 to the ancestral forms, and Gephyra dohrnii (see p. 382) is a link 

 connecting the order with the Actiniaria. 



There is no reason, however, for supposing that Gephyra 

 is specially related to this order, and, as pointed out recently 

 by Eoule,'^ the simple structure of the zooids of the Antipa- 

 thidea is more easily explained if they are regarded as primitive 

 forms. 



Gerardia (p. 406), from the Mediterranean, forms a horny 

 axial skeleton like that of the Antipathidea, but this genus is 

 probably a Zoanthid. 



Fam. 1. Antipathidae. — In this family the zooids have six 

 tentacles and six or ten mesenteries. It includes nearly all the 

 familiar genera, such as Stichopathes, Cirripathes, Antipathes, 

 Antipathella, Cladopathes, and Bathypathes. Schizopathes and 



^ Hickson, Nature, Ixxiii. 1905, p. 5. 

 ^ L. Koule, Bull. Mus. Ooianogr. Monaco, 1904, p. 3. 



