THE GROWTH OF THE CRAYFISH. 31 
liver (fig. 5, Lr); and, in the breeding season, the 
ovaries of the females, or organs in which the eggs are 
formed, are very conspicuous from the dark-coloured 
eggs which they contain, and which, like the exoskeleton, 
turn red when they are boiled. The corresponding part 
in a cooked lobster goes by the name of the “ coral.” 
Beside these internal structures, the most noticeable 
are the large masses of flesh, or muscle, in the thorax 
and abdomen, and in the pincers; which, instead of 
being red, as in most of the higher animals, is white. 
It will further be observed that the blood, which flows 
readily when a crayfish is wounded, is a clear fluid, and 
is either almost colourless, or of a very pale reddish or 
neutral tint. Hence the older Naturalists thought that 
the crayfish was devoid of blood, and had merely a sort 
of ichor in place of it. But the fluid in question is true 
blood ; and if it is received into a vessel, it soon forms a 
soft, but firm, gelatinous clot. 
The crayfish grows rapidly in youth, but enlarges more 
and more slowly as age advances. The young animal which 
has just left the egg is‘of a greyish colour, and about 
one quarter of an inch long. By the end of the year, it 
may have reached nearly an inch and a half in length. 
Crayfishes of a year old are, on an average, two inches 
long ; at two years, two inches and four-fifths ; at three 
years, three inches and a half; at four years, four inches 
and a half nearly ; and at five years, five inches. They 
