26 Dr. Reid on the Development of the Medusse. 



September 1845^ and the other two on the 11th of July 1846, 

 adhering to the lower surface of stones in pools near low water 

 mark. The stones were of a size which readily permitted them 

 to be conveyed home, where I have kept them up to the present 

 time. The mode I have followed in keeping these animals alive 

 is this. The stones to which they adhere are placed in vessels 

 of considerable size, supplied daily with water fresh from the 

 ocean, and the animals fed once or twice weekly with small 

 morsels of mussels, which they readily swallow. The first of the 

 three colonies consisted of between thirty and forty individuals, 

 and the largest was between two and three lines in length ; the 

 individuals composing the other two colonies were more nume- 

 rous and of somewhat larger size. 



After I had completed my examination of the structure of 

 these animals I discovered that they had been described by Sars, 

 first imder the generic name of Scyphistoma, and afterwards as 

 the larva of the Medusa^. 



Many of the larvse increased much in size several months after I 

 took them home, and the body of one that I measured was ^^rd of 

 an inch in length and J-th of an inch in diameter ; another was 

 y*2 ths of an inch in length and y^^^^^ ^^ ^^ ^^^ ^^ circumference. 

 As every part of their body is contractile, they can assume a great 

 variety of forms. The more common of these are represented 

 in PI. V. figs. 1, 2, 3, 4 and 5. Though almost all of them are 

 throughout of a grayish white colour, a few presented spots or 

 patches of a purple colour, which were sometimes observed to dis- 

 appear and reappear in the same individual. The tentacula are 

 generally from twenty-two to twenty-seven in number, and when 

 fully expanded are three or four times the length of the body. In 

 one that I measured the body was /yths of an inch, and the tenta- 

 cula l^f ths of an inch in length ; in another the body was g^ths, 

 and the tentacula g^ths of an inch in length. The mouth is very 

 dilatable and varies much in shape, but is most commonly qua- 

 drangular. When fully expanded it forms a round aperture oc- 

 cupying nearly the whole of the disc (fig. 5) ; at other times its 

 margins or lips are elongated and approximated so as to form a 

 considerable quadrangular projection (fig. 2 5). Its more com- 

 mon condition perhaps is that represented in fig. 3 a. 



The four round, equidistant and slight depressions placed be- 

 tween the mouth and margin of the disc are represented in fig. 2 a. 



The body and tentacula of the larva are composed of two di- 

 stinct layers, an internal and external. The internal layer chiefly 

 consists of nuclei and nucleated cells (PI. VI. fig. 19) of various 

 sizes, some of them containing a large number of nuclei ; while 

 the external is chiefly composed of a structureless substance with 

 ♦ Annales des Sciences Naturelles, torn. xvi. p. 321, 1841. 



