CRUSTACEA. 505 
cavities among the vertebrata.” The pigment is less a membrane than 
an amorphous matter diffused through the outer layer of the superficial 
membrane, which changes to red in the greater number of species on 
being immersed in alcohol, ether, acids, or water at 212° Fahr. 
‘The calcareous crust of the animal is thick, and in the dorsal region 
capable of great resistance ; their arms and legs are also of remarkable 
hardness ; but in the smaller species the shell is often thin, and of 
that crystalline transparency which permits of the functions of diges- 
tion and circulation being observed. Many species, which are quite 
microscopic, contribute colour to the sea—red, purple, or scarlet-— 
such are Grimothea Duperreii, and G. gregaria. 
Before the year 1823 it was not generally supposed that this class 
of animals was subject to change of shape in its larval condition, and 
during its progressive development ; but about this time a certain able 
microscopist clearly demonstrated that a minute nondescript kind of 
animal, called the Zoca Zaurus, was nothing more nor less than the 
young of a kind of Prawn that had just escaped from the egg. This 
able microscopist, Mr. Vaughan Thomson, of Cork, by many suc- 
cessive observations, and under the fire of much adverse criticism, 
satisfactorily established the truth of a metamorphic change taking 
place in many genera, and, in particular, in the common crab (Cancer 
menas); having succeeded in hatching the ova of this species, the 
product of which proved to bea true Zoea. That there are variations 
in this law of change has now been admitted, but that generally a meta- 
morphosis exists analogous to that of insects in the various genera 
of Crustacea with hardly an exception has been clearly established. 
The recorded observations of the eminent naturalist we have men- 
tioned, Mr. Vaughan Thomson, as well as those of Mr. Couch, of 
Penzance, Professor Milne-Edwards—and particularly those of the 
last mentioned, who is the author of perhaps the best general work 
extant on the Crustacea—are referred to as treating in detail on this 
interesting subject. 
As an illustration of this metamorphosis, we give figures of the Zoea 
Taurus in two states (Fig. 339), viz., 2, in the first stage ; and second, 
6, as the animal appeared on the fourth day after the first micro- 
scopical examination, and when it resolved itself into a kind of prawn. 
These drawings appear in Mr. Bell’s “ History of British Stalk-eyed 
Crustacea,” and were taken by that gentleman from the work of a 
Dutch naturalist named Slabber, who made the original observation 
in the year 1768, and published the result in 1778, from which time 
the subject had been allowed to fall asleep until revived by Mr. 
Vaughan Thomson. 
