398 Cc. O. WHITMAN. 
indicates a correspondingly higher functional importance. 
Carry this disparity in development and functional value to 
the extreme, and the result would be a single series of lateral- 
line organs on each side, as in the case of the Capitellide 
(Hisig). The ‘presence of several rows equally developed on 
each side appears to me to represent an earlier condition than 
_ that of a single row, since it is more easy to account for the 
disappearance of one or more rows than to explain their inde- 
pendent origin in animals that have had a common derivation. 
Assuming that some ancestral form possessed several series of 
lateral-line organs, we should naturally enough expect to find 
variation in the number of series preserved in derived forms, 
some perhaps preserving all, while others preserved only a 
part or none at all. This view seems to me the most 
satisfactory way of accounting for the occurrence of more than 
one series of lateral-line organs in the Amphibia and some 
Fishes. 
The structure of the segmental sense-organs of Clepsine is 
fairly shown in Figs. 2 and 8. The organ represents a bulb- 
like thickening of the epidermis, supplied with a branch of the 
lateral nerve of the corresponding body segment. The outer 
face of the bulb rises as a rounded prominence above the 
general surface; the inner, more strongly rounded face is 
cushioned in the connective tissue that intervenes between the 
epidermis and the ring muscles. Imbedded in this connective- 
tissue receptacle are a number (four to eight) of very large clear 
cells (p.), differing in no respect from the large cells found in the 
eyes. These cells are loosely placed around the bulb and nerve, 
and often one or more of them may be seen at a little distance 
from the bulb, either below it, alongside the nerve, or to one 
side. I have nothing to add to what is known about the 
structure of these peculiar cells, except that they are nucleated 
(a point disputed by Ranke). I regard them as the morpho- 
logical equivalent of the epidermal gland-cells (g. c.), and 
therefore as belonging primarily to the epidermis. At the 
base of the bulb, often extending to a greater depth than shown 
in Fig. 2, are to be seen in most of my preparations some rather 
