368 The Structure of the Annelids. 



and M. Leydig that we owe the best researches into the 

 nervous system of Annelids. The first chiefly directing his 

 attention to the external form of this system, and the second 

 to its histology. . . . M. Quatrefages has been so fortunate as to 

 find a stomato-gastric system of nerves, similar to that of the 

 Hirudinea. I have not been able to recognize it, but I am 

 sure that a negative result is not of great importance in these 

 difficult investigations. I am, however, astonished that the 

 combined efforts of other observers have been equally unsuc- 

 cessful. . . . The structure of the nervous system varies 

 astonishingly in the series of Annelids; the distribution of 

 nerve-cells particularly being subject to a host of variations, 

 which will be explained hereafter. In the ventral chain the cells 

 belong chiefly to the surface and the sides, as Leydig has 

 already noticed. The existence of large tubular fibres on the 

 dorsal surface of the nervous chain, so general among the 

 Oligochgeta, is confined among the Polychteta to a small 

 number of families (Capitellians, Aricians, Spiodians, Sylli- 

 dians, Eunicians), and even appear in some representatives 

 only of these families. 



The nerve terminations amongst the Annelids have only 

 been studied hitherto by myself, and by MM. Keferstein and 

 Kolliker. All these terminations appear related to the func- 

 tions of touch. The nervous expansions of the organs of sight 

 and hearing are little known, even in Alciope, notwithstanding 

 the researches of Leydig. In reference to this subject, I may 

 recal an opinion of Joh. Miiller, which has fallen into oblivion. 

 We owe to this great physiologist an excellent figure of the 

 central nervous system, and of the eyes of the Nereids — a 

 figure to which his successors have not added anything im- 

 portant. He does not consider the organ called a ciystalline 

 lens as a dioptric medium. He denies its transparency, and 

 regards it only as a terminal enlargement of the optic nerve. 

 Although the transparency of the crystalline body is in many 

 cases incontestible, the opinion of Miiller on the functional 

 value of this organ should not be rejected. The eyes of 

 Nereids and of most other Annelids appear destitute of all ap- 

 paratus for accommodation. Admitting that the percipient 

 elements are lodged between the granules of pigment, it could 

 be only objects at a determinate distance that could project 

 their images upon this choroid pigment, and the sight of the 

 creature must be very limited. This difficulty disappears if 

 we seek in the crystalline body at once a refractory medium 

 and a percipient organ, as we are almost obliged to do in the 



crystalline cones of the Archropoda 



Restoration of Mutilated Paris. — The observations of 

 Bonnet on the restoration of mutilated parts among the earth- 



