met with during a Sea Voyage. 597 



They are defined by Cuvier to be a class of " animals 

 swimming in the water of the ocean, in whose organisation 

 we can still perceive vessels, which, however, are generally 

 mere productions of the intestines, excavated in the paren- 

 chyma of the body." They are divided by him into the 

 Symplixia, Medusa?, properly so called, or the bell-shaped 

 sea nettles of our coast; and into the Hydrostatica?, those 

 provided with a natatory sac, or air vesicle. A more useful 

 arrangement, however, for practical purposes, is that of M. 

 Lesson, quoted in a note to an article on this subject in the 

 Cyclopaedia of Anatomy and Physiology. It consists in their 

 division into those possessing a solid axis, as the Vellella, 

 Porpita ; and into those composed entirely of a soft gelati- 

 nous moss, as the Physalus, Medusa, &c. This class being 

 subdivided into the simple, of which the second species affords 

 an example ; and into the aggregated, the body being com- 

 posed of more than one individual, or possessing suplement- 

 ary organs, as the air vesicle of the Physalus. 



The number of these animals now known is considerable; 

 Eschscholtz having, as stated by Dr. Coldstream in the 

 article to which we have referred, described 200 species. In 

 the degree of their organisation, they are found to differ 

 widely. The digestive organs consist, in those having a solid 

 axis, of an oval aperture leading into an elongated stomach, 

 with which the tentacula around the mouth communicate. 

 In those possessing an air vesicle, the digestive organ is a 

 sac situated below it, with which the tentancula are in con- 

 nexion ; and, in the Medusa?, the stomach forms a branched 

 cavity within the bell-shaped mouth ; and the oval apertures 

 are sometimes one only, situated between its leaf-shaped 

 processes ; sometimes dorsal at the extremity of each process ; 

 and in some cases there is a complete passage through the 

 mouth of the animal. In some of these animals, a nervous 

 system cannot be detected ; nor do the habits of the animal 

 render its existence probable, as is the case with the Physalus. 

 In the Vellella, I saw, in some specimens which I examined, 

 several delicate white cords external to the stomach, which 

 may probably constitute a rudimentary nervous system; and 

 in the Medusa?, some of which (as the M. aurita) have eyes 

 developed from the margins of their mantle, and highly 

 irritable tentacula, nervous cords are observed surrounding 

 the mantle and mouth, and having ganglions upon them, from 

 which those organs receive their supply. 



As it is only my intention to dwell upon one or two kinds 

 of these animals, which I have had an opportunity of examin- 

 ing, I will speak of the Physalus. This species (generally 



x x 3 



