26 Dr. Reid on the Development of the Medusae. 
September 1845_, and tbe 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 1 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 tv/ice 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 under the generic name of ScyphistumUy and afterwards as 
the larva of the Medusa^. 
Many of the larvre 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 ^th of an inch in diameter ; another was 
y^ 2 lbs of an inch in length and 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 of an inch, and the tenta- 
eula yf ths of an inch in length ; in another the body was g^ths, 
and the tentacula yyths 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 dise (fig. 5) ; at other times its 
margins or lips are elongated and approximated so as to form a 
considerable quadrangular projection (fig. 2h). 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 Natiirelles, tom. xvi. p. 321, 1841. 
