134 Selections. [No. 7, new series, 



1st. The " Gerkin-medusae" (Beroida) have generally an egg- 

 shaped or round body, with a large mouth, a wide stomach-cavity, 

 and 8 rows of swimming-membranes which run in regular lines 

 along the body. See fig. 8, plate v. They are very agile and vo- 

 racious animals pursuing other medusae in particular. Beroe, Leseu- 

 ria, Medea. 



2nd. The- " Band-medusae" (Callianirida) possess but a very 

 small mouth opening, and an extremely narrow stomach, but they 

 very often have seizing arms and side flaps, on which the swim- 

 ming-membranes are arranged. To this family belongs the well- 

 known Girdle of Venus ( Cesium Veneris) a band about the width of 

 three fingers, from four to five feet long, with a narrow mouth in 

 the middle of the beautifully iridenent band. See fig. 9, plate v. 

 Cesium, Callianira, Alcinoe, Cydippe, Eucharis, Mnemia. 



From the gelatinous substance of these animals it is no wonder 

 that we cannot be certain of any fossil remains of them. 



Class Tunicata. 



The animals form this class distinguish themselves from all others 

 by their highly unsymmetrical build. In the greater number of 

 families it is a simple impossibility to recognize a middle line or 

 axes round which the organs are placed in any regular form ; it is 

 only in the higher families that a lateral arrangement can be per- 

 ceived, and these not very distinctly. The bodies of the animals 

 are generally irregularly cylindrical, egg or wart shaped, without 

 any exterior sign of division into different parts. 



The outer covering of the body always consists of a loose skin, 

 which is more or less tough, and encloses the whole be dy like a bag 

 and possesses only two openings, one for the ingress of food and 

 water, the other for the exit of the same. This mantle, which is 

 sometimes gristly, sometimes like jelly or leather, is for the greater 

 part of its mass composed of true woody fibre or Cellulose, which 

 does not dissolve in acids or alkalis, and forms the hard constitu- 

 ent part of plants. The inner structure of this mantle has been 

 thoroughly examined ; it consists principally of clear foundation, 

 substance in which not only fibres and cells are to be found, but 

 often variously formed crystalline aggregations of carbonated lime. 



