MUSEUM OF COMPARATIVE ZOOLOGY. 169 
areas. By this process the elements of the ventral line, as well as those 
of the cord itself, are so changed as to give rise to abnormal appear- 
ances even in otherwise well preserved specimens. Such a crushed con- 
dition of the cord is figured by Bürger (Fig. 19). 
Strictly speaking there are no nerves arising from the cord. The 
fibres which branch from it are nowhere collected into a group worthy 
the name of nerve. In every second or third section one finds a few deli- 
cate fibrils arising from the nerve cord; some emerge from the dorsal 
surface and some from the median ventral cleft, and in both cases they 
pass off towards the lateral hypodermis (Fig. 101). They may be traced 
as far as the beginning of the hypodermis proper, but their ultimate fate 
is unknown. If these are not nerve fibres, I am at a loss to explain 
them, or to find other branches which may be nervous. Only once did 
I,find any evidence of a large process leaving the cord; in one cross 
section a process like those found cut transversely in the cord was cut 
longitudinally ; it passed out from above the lateral area and followed 
the course of the fibres already described, as far as the hypodermis. 
c. Anal Ganglion. 
Bürger has shown (p. 638) that the anal ganglion far exceeds the 
brain in'size, and is in no sense a small local thickening of the ven- 
tral nerve cord, but that it is a gradual differentiation of its poste- 
rior portion. In a total view (Plate VI. Fig. 89) one is unable to see 
any definite line of demarcation between the ventral nerve cord and 
the ganglionic enlargement which terminates it. There is seen to be 
rather a gradual increase in the size of the cord extending over a dis- 
tance of about 1.2 mm., and culminating at the posterior end, where the 
ganglion is abruptly rounded off. In some specimens the differentiated 
portion of the cord is deeply cut by cross furrows which give it a meta- 
meric appearance. Although these may be present at times when no 
external folding of the cuticula can be found (Bürger, 91, p. 638), they 
certainly do not indicate any metameric condition of this organ, since 
they vary in size and since there is no corresponding structure in them. 
The furrows are entirely wanting in most well preserved specimens 
(Fig. 9), and when present are simply due to a folding of the cord, such 
as occurs in other portions of its length as well, but is more prominent 
here on account of the thickness of the organ. 
A cross section through the anal ganglion (Plate VIII. Fig. 96) shows 
at once that the increase in size is due chiefly to the addition of a periph- 
eral layer of cells above the cord proper. On aecount of this inorease 
