AN ICHTHY0BDELL1D PARASITIC ON SAND WHITING. 39 
is a side view, the other two figures are ventral views. This series 
shows the change from the cylindrical form of the young specimen 
(fig. 3) to the slightly flattened sexually mature specimen 4 mm. 
long (fig. 4). The shouldered appearance of the body of the specimen 
9 mm. long (fig. 5) and its greatly flattened form are in striking 
contrast with the form of the younger specimens. 
PLATE 2. 
Fig. 6. — A medial sagittal section of a specimen 8 mm. long, showing 
the genital openings, bursae, oviduct, ovaries, spermatophore sac, and 
the relations of the ventral nerve cord and the ventral and dorsal 
blood-vessels in this region. Compare with fig. 12a. The male 
genital opening is seen at $ and the bursa leading into the 
spermatophore sac ( Sp . s.). The female genital opening is seen at $ 
leading into the bursa, which has the walls of its dorsal part plicated 
( B.gl .) to form the glandular part of the female bursa. The oviduct 
( Ovd .) has been cut at two places, where it leaves the junction of the 
ovaries and more dorsally where it is about to enter into the glandular 
part of the bursa. The sections of the ovaries (Or.) show ova in 
various stages of formation by the breaking down of yolk cells; the 
two spindles represent maturation divisions. The relations of the 
ventral nerve cord and ganglia 11, 12, 13 to the sexual organs are 
shown, and may be compared with the model depicted in fig. 12a. 
The ventral vessel ( V. v.) is seen lying free in the expansion of the 
ventral lacuna which contains the sexual organs in this region. The 
dorsal vessel ( D . v.) is seen as it is entering the dorsal lacuna. 
The degree of development of the circular and longitudinal body-wall 
musculature is displayed. B. gl. Glandular part of female bursa. 
C. m. Circular body-wall musculature. D. v. Dorsal vessel. L. m. 
Longitudinal body-wall musculature. N.gn. Nerve ganglion. Ovd. 
Oviduct. Ov. Ovary. Sp. s. Spermatophore sac. V.v. Ventral vessel. 
Fig. 7. — Diagram in relief of the Nephridial System in the testicular 
region of the body viewed from the ventral surface. The posterior 
end of the leech would be towards the observer. For the sake of 
clearness the somite is shown as consisting of the three primitive 
annuli. In order to show the segmental nature of the nepridial system 
one whole somite and its portion of the nephridial system is drawn, 
and parts of the preceding and succeeding somities with their portions 
of this system. The ventral and dorsal lacuna are shown, but neither 
the segmental nor the contractile lucunse. On either side the lateral 
nephridial canal is seen receiving branches of the fine capillary network 
of nephridial tubules which extend in the dorsal and ventral sides of 
the body. The lateral nephridial canals are shown giving off in each 
