THE LEECHES OF JAPAN. 377 
in the hind edge of the 15th annulus instead of the 13th, and 
the location of the genital pores between the 32nd and 33rd, 
and between the 37th and 38th rings. Passing to the poste- 
rior end of the body (fig. 55), we find here only three abbre- 
viated somites, the 23rd somite containing the full number of 
rings. Thus there are eighteen unabbreviated somites (sixteen 
in Hirudo) and eight abbreviated (ten in Hirudo). It is inter- 
esting to note that the abbreviated somites have been abbre- 
viated to very nearly the same extent as in Hirudo. As we 
have here two more complete somites than in Hirudo, we have 
106 annuli between the first pair of eyes and the anus. The 
nephridial pores occupy the same somites (six to twenty-two in- 
clusive) as in Hirudo, and hold homologous positions ; for the 
15th and 95th annuli are here homologous with the 13th and 
the 93rd in Hirudo. The 106th annulus is homologous with 
the 102nd of Hirudo. The 108rd annulus (99th of Hirudo) is 
plainly double at its margin, though single elsewhere ; and the 
102nd annulus is constantly thicker than the preceding ring, 
which indicates that it represents two rings consolidated. 
There is abundant evidence that the somites are not abbre- 
viated by a sudden and complete syncopation of one or more 
annuli; the process is rather a gradual one, consisting in the 
coalescence of two successive annuli. When a papillate an- 
nulus combines with a non-papillate, ag seen in the 103rd, the 
individuality of the latter seems to be suppressed, in subordi- 
nation to that of the former. In this case (103rd annulus) it 
is evident that the posterior half of the annulus represents the 
original papillate annulus, as shown by the position of the 
papille, and thus it becomes plain that two successive 
annuli of different somites may combine. 
Leptostoma edentulum (Pl. XIX) agrees very closely 
with L. pigrum having 105 rings, and sometimes a fragment 
of a 106th. The number and abbreviation of the somites are 
essentially the same. Only one difference requires mention 
here: in the 23rd somite, the 97th and 98th annuli are often 
not so plainly divided as the following rings of the same 
somite. This peculiarity is not apparent in L. pigrum, while 
