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 BUrger (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 maybe 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. 



Biirger 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 I'ounded off. In some specimens the differentiated 

 portion of the cord is deeply cut by cross furrows which give it a meta- 

 rneric appearance. Although these may be present at times when no 

 external folding of the cuticula can be found (BUrger, '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 account of this increase 



