492 THE MICROSCOPE. 



orders : A. stabiles (fixed), A. liber ce (free), and A. hydro- 

 staticce (hydrostatic). Cuvier classed them in two orders : 

 A. simplices and A. hydrostaticcv. They 

 are now, however, divided differently, 

 and arranged in groups according to the 

 peculiar mode by which they effect their 

 locomotion. A very interesting point of 

 connexion between this class and the 

 preceding is the interchange of form. 

 Some of the Zoophyta, as the Tubula- 

 riadce and the Campanulariadce, give 

 birth to a progeny which are in every 

 respect Naked-eyed Medusae ; while, on 

 the other hand, the young of the Medusae 

 are in their earlier stages stationary 

 polypes . 



The Medusce spread on the surface of the water a beau- 

 ful jelly-like mass, in form resembling an umbrella ; and. 

 by a continual contraction and opening out of this, they 

 swim freely about (Plate IX. c, d, e, h). They are all 

 more or less- phosphorescent. The Beroe, one of the family 

 Ctenophora, propel themselves with active ciliated arms. 

 The Physalidce haye an organ common to fishes, swim- 

 ming bladders, by filling or emptying which they rise or 

 sink, and move along in their watery home. 



The Medusoid family, Lucernaridce, has, from a mis- 

 taken view of its organization, been referred to the class 

 Actinozoa : Milne-Edwards has, however, placed it in a 

 sub-class, under the name of Podactinaria. In the 

 Lucemaridoe the body is cup-shaped, about an inch in 

 height, terminating in a short foot-stalk. Round the 

 distal margin of the cup arise a number of short tentacles, 

 which are disposed in eight or nine turfts ; in Carduella 

 they form one continuous series. Their free extremities 

 appear sucker-like, and the whole organism is semi-trans- 

 parent, of a gelatinous consistence, and variously coloured. 

 The cup, viewed from above, presents in its centre a four- 

 lobed mouth, which is seen to form the free extremity of 

 a distinct polypite, occupying the axis of the entire 

 hydrosoma. Its gastric region exhibits a number of 

 tubular filaments, arranged in vertical rows dipping ic.to 



