616 CLASS X. 
stomach, and are named crab’s-eyes (ocul’ s. lapides cancrorum), 
supplied the matter from which the new shell acquired its hardness. 
These little stony substances are cast off with the old tunic of the 
stomach, and being freed from their capsules come into the cavity 
of the stomach, where they are broken up and partly dissolved. 
Thus it is possible that the calcareous matter, taken up into the 
blood, may be useful for the secretion of the hard shell (V. BAzr). 
The part, however, which the crab’s-eyes take in the secretion 
cannot be great, when we compare their weight with that of the 
calcareous matter in the shell. During the time that the shell is 
still increasing in hardness, no new crab’s-eyes are produced; but 
only after the shell has attained its greatest hardness is calcareous 
matter again secreted on the walls of the stomach, and new crab’s- 
eyes again appear. Thus the production of crab’s-eyes would appear 
to be a vicarious secretion; a secretion of such constituents of the 
blood as, if too abundant, would be injurious to the organism, like 
the secretion of urine for instance, but with this difference, that the 
calcareous matter is not set at liberty shortly after its secretion, but 
remains accumulated for a long time in continuance}. 
The power of restoration or reproduction is very great in this 
class, so that even feet, amputated or broken off, are replaced by 
new ones. 
We will now speak concisely concerning the organs of animal 
life. The nervous system consists, as in articulate animals generally, 
of a cerebral ganglion above or in front of the cesophagus and of a 
ventral cord, which is formed of a greater or lesser number of ganglia 
connected together by two filaments. Originally every nervous 
ganglion consists here, just as we remarked formerly on the ringed 
worms, of two lateral portions. In some crustaceans this separation 
of the nervous ganglia persists even in the adult state, as in Cyamus, 
Talitrus and Idotea; the lateral parts are merely connected by a 
transverse commissure. In the Oniscides the two nervous filaments 
of the cord le quite apart from each other, and the ganglia still 
indicate evidently, by their compressed broad form, their original 
1 Already in the first edition of this Handbook I offered essentially the same 
opinion respecting the use of the secretion of crab’s-eyes, 1. bl. 410. Comp. on this 
subject V. Barr Ueber die sogenannte Hrneuerung des Magens der Krebse u. 8. w. in 
MUELLER’S Archiv, 1834, s. 510—523, and DuLK’s chemical investigations, ibid. 
Ss. 523—527, but especially GistaRLEN, MUELLER’S Archiv, 1840, 8. 432—440. 
