SEA-FISHERIES LABORATORY. 89 
sucker relatively small, and without radial thickenings 
or chitinous hooks. Intestine with two branches, and 
without lateral diverticula. Genital opening common, in 
the middle line immediately behind the pharynx. 
Vagina single and unpaired, opening on the ventral sur- 
face to the left of the common genital aperture. Testis 
single. One to two millimetres in length. 
The specimens taken from Dogfish caught in the 
open sea were larger than those inhabiting the Port Erin 
tanks. I give measurements from the former examples, 
but the ratios of the dimensions of the various organs tu 
the length of the body are the same in both series of 
specimens. 
~ Length: 2mm.; Breadth: 12mm. 
Transverse diameter of anterior sucker: 0°14 min. 
Transverse diameter of posterior sucker: 0°3 mm. 
Transverse diameter of pharynx: 0°23 mm. 
Transverse diameter of cirrus sac: 0°25 mm. 
Diameters of ovary: 0°35 x 0°32 mm. 
Diameters of testis: 0°5 x 0°23 mm. 
Mature, shelled eggs were not seen. 
The body of the animal is flattened dorso-ventrally, 
and is elliptical in shape. In fixation it usually contracts, 
so that it becomes arched in the longitudinal direction, 
and with the convexity dorsal. This leads to some degree 
of distortion, and the relationships of the various organs 
in the preserved specimens are not exactly similar to 
those in the worms examined in the fresh condition. All 
the specimens so far seen are evidently immature. 
The Suckers. 
There are no lateral suckers or other accessory 
organs. The anterior sucker is elongated transversely, 
and its opening may be very different in shape. Usually 
G 
