280 NATURAL HISTORY. 



Mediterranean, is a long, slender, narrow, strongly -com pressed, very agile creatui-e, rather enlarged in 

 front and behind. There are two tactile filaments, each one with an offshoot, and they are fixed to 

 the buccal or month region, which is carried downwards. It is covered with moving cilia, and 

 four ranges of motile organs, and four vessels are noticed on the xipper part of the body. Four 

 other vessels are in the lower part, and they are in communication. The graceful undulating 

 movements of this Cestum have always excited the admiration of those naturalists who have had 

 the good fortune to see them. 



Some of the Ctenophorse are very abundant, and hundreds of the group, characterised by 

 having a bell-shaped body, and belonging to the Eurystomse, are caught in the Northern seas when 

 fishing-nets are brought up. The common Beroe of the British coasts is one of them, and so is the 

 Rosy Idya of the American Seas. 



All the Cteiiophorae are produced from eggs, and the young swim in the egg long before they are 

 set free ; they have the flappers of great size in relation to the rest of the body. An examination of 

 the development of the young of the different great groups proves that certain structures, which last 

 on in the less complicated forms, are transient in the higher ones. 



ORDER DISCOPHORA. THE MEDUSAE, OR JELLY-FISH. 



Everybody is familiar with the appearance of the large Jelly-fish which move so gracefully by 

 expanding and contracting their umbrella-shaped discs, and on the surface of which four more or less 

 circular coloured patches are to be seen. Hundreds occur off the British shores, swimming with the 

 tide, and rising and sinking in the clear sea in the summer. They are semi-transparent and 

 almost colourless when seen by daylight, and some of them are luminous at night. When one is 

 caught by the hand, unless care be taken, the fingers enter its tender substance, and it falls motionless 

 into the water. And when one is found stranded and dead on the sand, the edge of the disc is seen to 

 be lobed and furnished with a fringe of thread-like tentacles ; the circular spots on the top are 

 also visible, and so are numerous markings, like lines, eight often being principal, passing from 

 the top of the disc to its circumference, and uniting in a canal which passes all round the edge, 

 just within the substance of the Jelly-fish. 



On turning this Discophora or Medusa on its back, and looking at the under surface of the disc, 

 a central opening is to be found, into which the finger can pass. This is the mouth, and the passage 

 leads through the substance of the disc to a cavity, the stomach, which is surrounded by the four 

 coloured circular spots. 



The substance of the disc has an outer very delicate skin covered with cilia, and on the 

 under surface of the disc muscular fibres stretch from the margin to the edge of the mouth. In some 

 very large kinds* the substance itself is rather tough; and yet Agassiz states that one which weighed 

 341bs. being left to dry in the sun for some days lost T Vo tns f ^ original weight. Such an one would 

 be seven feet in diameter without its tentacles ; but from one to five feet are the common sizes. Hence 

 these great discs principally consist of water, and it is held in the meshes of a connective tissue, 

 which contains cells possessing amoeboid movements. The skin which lines the mouth and the 

 stomach also enters the four circular cavities, and also the canals which radiate from the stomach in 

 the disc substance, and reach the circular canal. 



At the bottom of each of the notches on the edge of the disc which separate it into lobes is a 

 small oval body containing calcareous matter on a minute stalk, the cavity of which is continuous 

 with one of the radiating canals just noticed. Pigment may also exist about the little body, which 

 has been called a lithocyst, and has been deemed an organ of special sense for hearing or seeing, or 

 both. A membranous covering usually protects the so-called eyes. 



The entrance to the mouth is in the midst of a part of the body which is denser than the rest, 

 and, indeed, the disc may be considered to be an appendage. It is made up of four parts, which may 

 be divided so as to present eight radiating arms, in the midst of which is the passage to the 

 stomach. This part, which hangs down, when the disc is in motion, is called the hydranth. The 

 circular spots are reproductive organs, and the eggs escape from them into the stomach, and pass forth 

 through the mouth. In some kinds the stomach has pouches, and in all, the radial canals whether 



* Cyanea arctica. 



