616 CLASS X. 



stomach, and are named crab's-eyes (oculi s. lapidcs cancrorum), 

 supplied the matter from which the new shell acquired its hardness. 

 These little stony substances are cast off with the old tumc 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. BAER). 

 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 1 . 



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 oesophagus 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 Gyamus, 

 Talitrus and Idotea ; the lateral parts are merely connected by a 

 transverse commissure. In the Oniscides the two nervous filaments 

 of the cord lie 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, I. bl. 410. Comp. on thin 

 subject V. BAER Ueber die soyenannte Erneueruny des May ens der Krebse u. s. w. in 

 MUELLER'S Archiv, 1834, s. 510 523, and DULK'S chemical investigations, ibid. 

 s . 523527, but especially (ESTERLEN, MUELLER'S Archiv, 1840, s. 432440. 



