1104 The Segmental Sense-Organs of the Leech, [November 
THE SEGMENTAL SENSE-ORGANS OF THE LEECH 
BY DR, C. O. WHITMAN. 
3 Mesa only sense-organs hitherto known in the medicinal leech 
are the five pairs of eyes and the so-called “ goblet-shaped” 
organs located in the edge of the lip (cephalic lobe). A number 
of writers have noticed and described some small spots occurring 
on every fifth ring of the body; and one author has suggested 
that they may have a respiratory function. But no one, so faras 
the published accounts inform us, has intimated that they repre- 
sented sense-organs, or suspected that they were the serial homo- 
logues of the eyes themselves. These spots, when examined 
closely with a low magnifying power, will be found to be slight 
elevations with rounded summits, and for this reason and becaust 
they are regularly disposed on the first ring of each segment 
(somite) they may be called segmental papillæ, a name which 
does not prejudge the question of their function. In our large 
pond leech (Macrobdella) these papillæ are comparatively small; 
and the same may be said of the medicinal leeches of Europe 
and Japan, and their nearest allies, Hamopis and Aulostoma. In 
some of the Asiatic medicinal leeches, for example, those 
Saigon, Singapore (H. maculosa), Java (H. javanica) and Ceylon 
(H. multistriata), they are much larger and have an oval form 
with a median ridge or crest. In the land leeches they are very 
conspicuous, having the form of small cones with rou 
summits. 
In all the ten-eyed leeches of Japan, including b 
fresh-water forms, twelve of these papilla are foun 
ring of each complete somite, six on the dorsal and six 4 
tral side. In most of the medicinal leeches, however, 45 well e 
Hæmopis, Aulostoma, Macrobdella, &c , there are eight 0 
dorsal side and six on the ventral. , as tea ae 
_ A careful study of the arrangement of these papilla in @ ut 
number of species, and of their histological structure, has o 
out in a most conclusive manner their serial homology ee 
eyes ; and has led, indirectly, to the recognition of ee sal 
tant points in regard to the metameric composition of t er 
of the leech. The accompanying diagram will enable a 
brief. The eyes are represented by five pairs of large ar the 
the segmental papilla by smaller dots. The numerals: sa 
oth the landand | 
d on the fist 
on the vel 
