clviii Introduction. 



plates. An otolithic cysticle, sometimes called the *^ ctenocyst/ is 

 situated at the point of junction indicated. (See, for the doubtful 

 character of the nerve-system, Claus, Zeitschrifb fiir Wiss. Zoolog-ie, 

 1864, p. 386.) The Ctenophora are hermaphrodite, the testes and 

 ovaries being placed on either side of each of the eight canals, cor- 

 responding with the rows of swimming plates. The development 

 of the embryos, which are as in Anthozoa set free through the 

 mouth, is ordinarily simple ; but they are in some instances fur- 

 nished with provisional ciliated and other organs. , 



Class, Anthozoa. 



Coelenterata, of sub-columnar form, with their mouth surrounded 

 by a corona of tentacles, the number of which is either four or six, or 

 some multiple of four or six, contrasting herein, as in so many other 

 points, with the pentamerous Echinodermata. Their opposite imper- 

 forate extremity is ordinarily fixed ; and they are ordinarily social. 

 They are all marine, and may l^e no more than a line in length and 

 breadth. With the exception oi Actinidae and Cerianihidae , all have 

 the external integumentary system more or less indurated by inor- 

 ganic deposits, which form ' the coral structures.' These structures 

 are ordinarily divided into two classes, accordingly as they have been 

 supposed to be cuticular formations or ' foot secretions,' when they 

 have been called ' sclerobasic -^ or to be due to deposition within 

 the tissues, when they have been called ^ sclerodermic;' but doubt has 

 been thrown on the soundness of this distinction by Kolliker (see 

 Icones Histiologicae, ii., pp. 1 17-170). The body cavity is not only 

 directly continuous with the cavity of the stomach by means of an 

 orifice at the bottom of this latter cavity, but it is also continued 

 upwards round the outside of the stomach, which is freely suspended 

 in it by means of lamellar mesenteries. These lamellae divide the 

 body cavity into a series of radially-arranged chambers, which again 

 are prolonged upwards so as to be continuous with the interior of 

 the tentacles. The interior of the tentacles may communicate 

 directly with the exterior by perforations placed at their lips, as 

 may also the general cavity of the body by peripherally-placed aper- 

 tures called ^ cinclides.' In Cerianthus and PeacMa, the axis of the 

 foot may be perforate. 



The Anthozoa are, with the exception of Cerianthus, dioecious. 

 The generative organs are developed in the mesenterial lamellae. 



