THE LEECHES OF JAPAN. 353 
The ground colour of the more typical specimens is brownish 
olive above and pale or yellowish olive below. The typical 
markings of the dorsal surface are five longitudinal yellow 
stripes, bordered on each side with very dark brown or black, 
and usually interrupted (figs. 17 and 19) or blurred (fig. 11) 
on the first or papillate ring of each somite. The median 
stripe, which is the broadest and brightest, widens a little on 
the cephalic Jobe between the eyes, and usually terminates 
behind in a more or less semicircular patch on the acetabulum. 
The only markings below are two irregular, often nearly 
obsolete, dark brown streaks bordering the yellow margins 
(figs. 13 and 20). 
The figures of Pl. XVIII have been selected with a view to 
showing both the degree and the method of variation in colour- 
markings. The differences in this respect between figs. 18 
and 19 are so extreme that it seems at first sight difficult to 
reconcile them with the fact that the figures represent specifi- 
cally identical individuals. The specimen represented in fig. 
18 was examined closely and found to agree in every par- 
ticular, except colour, with the common Medicinal Leech of 
Japan. It was found in a stream that flows alongside the 
shallow lake known in Tokio as Shinobazu no Ike, where 
the common Leech is extremely abundant. Among hundreds 
of Leeches collected at many different times from the same 
locality this was a solitary example in colour, and hence must 
be regarded as an individual colour-variety. 
An interesting question now arises. Are these colour- 
varieties mere variations or modifications of what I have 
described as typical? or are they so many different patterns 
having no sort of relationship with one another? A closer 
inspection of the figures shows that the first of these questions 
must be answered in the affirmative. In fig. 18 the olive 
shades have almost wholly disappeared, leaving the ground- 
colour a dull dingy yellow, marked by six irregular dark 
stripes. If the yellow ground between these stripes be re- 
garded as corresponding to the yellow stripes of most speci- 
mens, as plainly indicated by the position of the segmental 
