No. 2.] THE MORPHOLOGY OF DERO VAGA. 149 
segments in the anterior region are shorter than those follow- 
ing, and all the segments have a more or less distinct secondary 
annulation. 
(b) Sezae. 
The first segment bears no setae. The second, third, fourth, 
and fifth bear each two bundles ventrally, containing from eight 
to twelve long slender setae with bifurcate tips. The following 
segments bear four bundles — two dorsally and two ventrally. 
The dorsal bundles contain two peculiar palmate setae and two 
capilliform setae. The ventral bundles contain four or five bi- 
furcate setae resembling those in the anterior segments, but 
being somewhat shorter and thicker. In sexually mature indi- 
viduals the ventral setae are absent in the sixth segment. 
In cases of fission and regeneration the ventral setae form 
before the dorsal, and the setae in the anterior segments 
whether in the head or tail are always the first formed. 
(c) Epidermis. 
The epidermis is composed principally of hexagonal colum- 
nar cells, the width of which is about twice the height. These 
cells have large nuclei and are covered externally by a thin 
chitinous cuticle. 
In addition to these cells there are found sensory cells and 
gland cells. The sensory cells are spindle-shaped and have 
large nuclei compared to the size of the cell. The nuclei stain 
much more deeply than those of the ordinary epidermal cells. 
From the outer end of the cell projects a long, stiff hair or 
bristle (Figs. 10, 14-16). The sensory cells may occur singly 
or in groups. In the latter case the epidermis shows a hemi- 
spherical elevation at that spot. The sense organs will be 
discussed in more detail later on in this paper. 
The gland cells are goblet-shaped and often are found with 
granular contents. They are more abundant in the head region 
than elsewhere. 
The epidermis is thicker on the ventral side than on the 
dorsal and the cells multiply rapidly where a fission zone forms 
and at the posterior end of the worm. The epidermis of the 
