208 CcdliohdeUa lophii 
segments. The 12th segment though not bearing vesicles is also divided 
into 6 annuli. 
(B) Anal Region : 
3 annuli, each of which is a complete segment, the anus opening 
between the last and the last but one. 
(C) Posterior Sucker : which probably represents 7 segments. 
Total for the whole body 34 segments. 
Nervous System. There is, of course, a ventral nerve cord with 
ganglia along the chain. The foregoing conclusions concerning seg¬ 
mentation (not annulation) are based principally on the consideration 
of these ganglia. Whitman (1885) was the first who gave an account 
in which he distinguished the number of segments in leeches. In the 
common leech {Hirudo) he made this number 23. Bourne (1884) also 
regarded the ganglia of the neck mass and of the posterior sucker 
respectively as one complete ganglion, making a total of 23 ganglia. 
But these are undoubtedly large ganglion masses formed by the fusion 
of several ganglia. Leuckart (1894) considers that the anterior ganglion 
is equivalent to 5 ganglia, while the posterior ganglion is equivalent to 
7 ganglia. 
But Whitman (1889) now shows us that the upper part of the 
anterior ganglion (oesophageal ganglion) indicates a separate segment. 
23 — 24-5 + 7-1-1 = 34 ganglia. 
Respiration. Respiration is carried on by means of rounded vesicles 
protruding from the abdominal portion of the body. Considering that 
Van Beneden and Hesse (1863) mention two different numbers of pairs 
of vesicles and figure yet a third number, it is no wonder that there 
is some confusion on the subject. Blanchard states that there are 
12 pairs, and so there may be in other specimens. But I am quite 
prepared to agree with Johannson that there are eleven pairs in Callio- 
bdella, and most certainly so in C. lophii, which is not one of the numbers 
given by Van Beneden and Hesse. These vesicles rise and fall. They 
are rudimentary branchiae corresponding to the large external branchiae 
of Branchellion, and similar to the hemispherical vesicles of Cysti- 
hranchus. According to Quatrefages (1852) these appendages do not 
receive the blood contained in the vessels but only the lymph, which 
becomes diffused so that the respiration is truly lymphatic. 
Pigment. The blackish-brown star-shaped pigment cells which 
are characteristic of Piscicola and Cystibranchus are absent in this 
