THE LEECHES OF JAPAN. 385 
the first pair of eyes. The spots of the lateral stripe some- 
times blend in a similar manner. 
The spots occur on the 2nd and 4th annuli of the somite, 
so that an interval of one annulus (3rd) alternates with 
one of two annuli (5th and Ist). Thus ten spots, two in 
each stripe, are found on each of the unabbreviated somites. 
This is the typical arrangement of the spots in specimens 
found about Tokio; but it is occasionally modified by the 
interpolation of small spots, as shown in figs. 22 and 27 d. 
In specimens obtained from a small lake (Junsainuma) near 
Hakodaté, in Yezo, the interval of one annulus is filled by a 
spot, so that three spots occur on successive annuli, followed 
by two annuli without spots (fig. 24 d). This arrangement 
may occasionally be modified by filling up some of the intervals 
of two annuli. 
The entire absence of these spots in the median stripe of 
some individuals, the variations resulting from the filling up of 
the intervals, and their confluence at the anterior end of most 
specimens, all suggest that they may be regarded as remnants 
of yellow stripes, such as are seen in H. nipponia. 
Qn the acetabulum one or more broad median patches of 
yellow are seen, which represent parts of the original stripe, or 
perhaps confluent spots. These patches are bordered laterally 
by a narrow wavy line of dark brown or black, precisely as are 
the spots on the body. 
In many specimens dark flecks are scattered along each side 
of the median stripe (fig. 23). 
The ventral surface is generally a dull orange yellow, marked 
with broad marginal stripes of dark brown with interspersed 
flecks of black, and with six or more narrow and much broken 
intermediate brown stripes. The ground colour of this side 
often varies towards the olive (fig. 27 v.) and brown shades 
(fig. 24 v.). 
Genital Organs.—The penis lies on the left side of the 
nerve-chain, just behind the sixth pair of ganglia. The vagina, 
consisting of a saccular and a tubular portion (fig. 67 v.), lies 
on the right side of the nerve-chain, reaching from near the 
