134 THE EUCRATEA. 



The actual orifice for the emission of the animal is at 

 the upper and outer part of this membrane, where the 

 integuments are protruded by gradual evolution, 

 according to the universal rule in this Class of 

 Zoophytes, in three successive stages, which resemble, 

 when fully protruded, the slides of a telescope. The 

 first of these is horny, and has a sort of spine on the 

 inner margin ; the second, of about the same length, 

 is of the most delicate filmy transparency, and has its 

 margin surrounded by a sort of scolloped frill, com- 

 posed of short ribs united by a waved membrane,* 

 and diverging at right angles to the tube. From this 

 projects the third, which generally bulges more or 

 less at the back or outer side, where the orifice of 

 the rectum is situate. A bell of twelve ciliated 

 tentacles, nearly as long as the interior of a cell, crowns 

 this last evolution ; and the whole when extended to 

 the utmost, is more than commonly prominent. 



Let us now examine the anatomical structure of 

 this beautiful animal. The tentacles are slender fila- 

 ments, set with cilia, which are seen to be hairs of 

 extreme tenuity, and at least five or six times as long 

 as the diameter of the tentacle. This, however, can 

 be detected only by using a high power (say 200 

 linear) with delicate manipulation, when the ciliary 

 action is suspended ; as when the tentacles are in the 

 act of emerging. The waves of the ciliary motion 

 run (as usual in Polyzoan zoophytes) up one side of 



* This marginal frill is, I presume, analogous to those fine setse, con- 

 nected by a membrane, which Dr. Farre has described as surrounding 

 the sheathing tube of the polype, in Bowerhankia densa. (Phil. Trans. 

 1837. 



