100 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
not fat, for they are not blackened by osmic acid, nor do they seem to 
be pigment, since the granules are comparatively large and at the same 
time quite variable in size. Racowitz (’95) found ameeboid cells de- 
positing pigment in the region of the ciliated groove, but I have no 
reason to think the condition in the present instance is due to the same 
instrumentality. 
4, CILIATED GROOVE. 
The ciliated grooves lie on the posterior margin of the cephalic lobe 
behind the posterior eyes (Plate 3, Fig. 20). A fold of the anterior 
margin of the cephalic segment extends forward a short distance over 
the cephalic lobe, to which it is attached in the median plane, and also 
at a point just lateral to the eyes. On the ventral wall of the pockets 
thus formed there is an elongate eminence or ridge about 0.5 mm. long 
and 0.2 mm. wide, with the long axis transverse to the body. Along 
the crest of this ridge lies the ciliated groove. The ridge is formed by a 
thickening of the non-ciliate hypodermis, the cells of which are very long 
and arranged with their distal ends directed toward the crest of the 
ridge, thus producing in cross section the figure of an inverted V. The 
space between the cells which form the ridge is occupied by the ciliated 
cells. The cuticula over these cells is very thin, and the cilia project 
through it, forming a narrow band along the bottom of the groove. The 
nuclei of the ciliated cells lie much deeper than those of the non-ciliate 
cells on either side of them. The organ is innervated by the nerve 
XIII. There are no glands in the hypodermis of this region, but the 
overhanging fold of the cephalic segment is richly supplied with them. 
5. VENTRAL NERVE Corp. 
The structure of the ventral nerve cord can best be set forth by de- 
scribing transverse and longitudinal sections of it. A transverse section 
between ganglia (Plate 5, Fig. 31) shows that there are three longitu- 
dinal connectives ; two large lateral and symmetrical ones, and a small, 
more dorsal median one. Each connective is enveloped by the fibres of 
the inner layer of neuroglia, which thus separates the three connectives. 
In preparations successfully fixed in either the corrosive sublimate or 
osmic acid mixtures, the cross section of the connectives shows nothing 
but the circular outlines of the cut nerve fibres, with their contents and 
a few neuroglia fibres penetrating the connective from the sides. The 
fibres vary greatly in size, from the large giant fibres, which are one 
