74 Observations upon the Habits, Structure and | February, 
the merest traces of a cleft or opening, as seen in the center of the 
“button” of this end. 
The sides of this canal, throughout its entire length, are 
marked by small, black, roundish pigment spots, which are some- 
times aggregated into small clusters, but more commonly are 
scattered along at varying intervals from each other. In the sub- 
stance of the anterior, beak-like extremity, and just in front of 
the end of the central canal, there is a large pigment spot which 
is generally thought to represent the rudiments of a median eye ; 
but if it does not, then Amphioxus is entirely lacking in such an 
organ. Prof. Quatrefages, in 1845, described and figured a 
prominent protuberance as existing upon the side of the cord at 
this end, and claimed that it showed at its extremity a distinct 
and rather well-developed crystalline lens, thus representing a 
stalked eye, with the staik pointing towards the anterior extrem- 
ity of the body; but later observers have failed to confirm his 
observations in this respect, the only short protuberance which is 
formed along this portion being considered as representing, as 
already mentioned, an olfactory rather than an optic organ. 
The peripheral portion of the nervous system consists of a suc- 
cession of pairs of nerves given off from the upper part of the 
sides of the chorda dorsalis along its entire length. They originate 
in single roots, and arise at intervals corresponding to the divis- 
ions between each two of the muscle plates. With the excep- 
tion of the first and last pairs, all the nerves are of nearly uniform 
size, and, with the same exceptions, they pass outward and down- 
ward branching two or three times in their course, to be distributed 
along the middle and lower portions of the sides of the body. 
Besides the lower branches, each of these nerves sends off, at a 
short distance from its origin, a branch which proceeds upwards to 
the dorsum of the animal, Fig. 6, Pl. u. The nerves, which form 
the first pair, arise anterior to the body muscles and from the 
anterior portion of the head of the chorda. They are quite large 
at their bases, and extend straight forward from the sides of the 
chorda towards the anterior end of the body, dividing in their 
course into a large number of branches which are distributed 
above and below, and all about the extremity of the notochord. 
These branches terminate, or at least many of them do, in the 
cells of the exoderm, or else in small bell-like knobs which are _ 
wedged in among the exodermic cells, and resemble them very 
1 Annales des Sciences Naturetiei 3m™me série, Zoologie. Tome qme, pe: k = 
oe. - 10-13, 8vo Tora, a : ip ee eee . 
