28 
ORDER— DIGENEA, van Ben. 
Sub-Order — Gasterostomata, Odhner. 
Family — Gasterostomidce. 
Genus — Gasterostomum. 
Gasterostomum gracilescens (Rud.) (Plate I., figs. 1, 2, 3.) 
Rudolphi, C. A., Distoma gracilescens. " Entozoorum Synopsis," 
page 409 (1819). 
This well-known parasite of the Angler is very common on this 
coast. In every Angler examined the pyloric caeca and the stomach 
were much infested, and in a less degree, the whole of the remainder 
of the intestine. Cobbold* first recorded this species from Britain, 
and since his writings I can find no further British record of the 
adult worm, It must, however, be very abundant, judging from 
the enormous numbers in each fish, certainly several hundreds, and 
so crowded together that the gut looks quite brown from the eggs 
contained in these worms. Olssont estimates the number of 
worms in each fish to be 1,000-2,000. 
My specimens (fig. 1) measure, on an average, about 6 mm. in 
length (Cobbold's specimens i inch). They are colourless, except 
for the brown eggs, and broader at the head than at the tail end, 
but are continually changing their shape when alive. The whole 
body is covered by minute spines. The anterior sucker is round, 
measuring 0-40 mm. across. The oral ventral sucker is 0-30 mm. 
across. The latter, which occurs at about the first quarter of the 
body, leads to a small sac-like intestine full of food granules. The 
excretory vesicle is a long and narrow sac reaching to nearly the 
centre of the intestinal region. It contains a highly refractive 
granular substance. The testes are ovate bodies lying obliquely 
one behind the other behind the intestine. From the inside of 
each a vas deferens is given off, and these unite in a single short 
canal leading to the vesicula seminahs enclosed in the cirrus sac. 
The cirrus sac is long and narrow, and lies in the posterior part 
of the body. In it are the somewhat triangular, simple and very 
small vesicula seminalis and the pars prostatica, the latter forming 
a narrow canal into which open the prostate cells. The whole of 
the space surrounding this, inside the cirrus sac, is a mass ol 
gland cells. The male duct opens into the genital sinus, ana 
the genital pore liesjittiiej)^^^ 
* OoM>old,T. S., "Observations on Entozoa, etc." Trans. Linn. Boo, London, XXU, 
^STi "Entozoa, iakttagna hos Skandinaviska Hafsfiskar." Lunds. Univ. 
ArskriCt., torn. IV., page 55 (1868). 
