590 WHITMAN. [Vou, II. 
first appear, there is no escape from the fact, when we once 
understand the structure of the eye in Clepsive. A vertical 
section in the plane of the optical axis reveals the com- 
pound nature of the eye, and the identity of its structure with 
that of the segmental sense-organs. Here stands the tactile 
part of the organ, an exact copy of every feature seen in the 
corresponding part of a segmental sense-organ; and below and 
behind, but in continuity with the tactile portion, lies the mass 
of visual cells. The common nerve runs up in front of the 
visual cells, dwindling gradually in size as its fibres pass to the 
cells, and at length it is lost in the tactile cells. The main 
features of this eye have been known to me for about two years, 
but it did not seem best to hasten the communication of the 
facts before giving the whole subject careful study. The sense- 
hairs were first clearly demonstrated in WVephelis, and next in 
both the young and adult of Clepszme. The nerves supplying 
the eyes and sense-organs of the head arise in Branchelliopsis 
and C/lepszne from the five sub-cesophageal ganglia. 
12. In Azrudo, the visual cells are symmetrically placed 
around the axza/ nerve fibres, and no tactile cells are developed; 
in Clepsine and Hementeria, the visual cells are developed only 
on the posterior side of the nerve, while the tactile cells are 
grouped above and in front. In Wephelis the nerve is again 
axial; in Branchelliopsis it is eccentric, as in Clepsine, and there 
are comparatively few visual cells. 
13. Both the eyes and the segmental sense-organs develop 
as local thickenings of the epidermis. At first the cells are 
alike in form, size, and structure. About the time the pigment 
begins to appear, the two sorts of sense-cells begin to show 
a difference in size, and an indistinct boundary line appears 
between them. 
14. The metameric arrangement of the sense-organs of the 
fTirudinea is a matter of more importance than the latest writer 
on the subject, Mr. Apathy, appears to realize. The limits of 
this paper do not permit me to review the arguments which this 
young naturalist has entombed in a preliminary report of about 
eighty pages (portentous dimensions !). I am compelled to re- 
mark, however, that this author has not been sufficiently careful 
in presenting the views of others. As one out of many instances 
that might be cited, the following is characteristic. I am rep- 
