288 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Distomum ocreatum Molin. 
[Plate 35, figs. 16-24, U. S. N. M. No. 6510.] 
Two lots of distoma, the first collected July 14 by Prof. II. M. Kelly from intestine of the pollock 
( Pollachius virens), the second collected August 29, from the bake ( Merluccius bilinearis), agree closely 
with the species obtained from the blue-fish. (Notes on Trematode Parasites of Fishes, Proc. U. S. 
National Museum, vol. xx, pp. 514-515, pi. lii, fig. 13.) 
For purposes of comparison I give the following measurements : 
Measurements . 
No. 1. 
No. 2. 
No. 3. 
Length, including appendix 
3. 66 
1.36 
1.26 
excluding appendix 
2. 88 
1.26 
1.06 
Breadth, anterior 
0. 40 
0. 19 
0. 19 
median 
1.05 
0. 37 
0. 33 
0. 14 
0. 10 
Diameter of oral sucker 
0. 30 
0. 18 
0. 15 
ventral sucker 
0. 34 
0. 20 
0. 15 
0. 17 
0. 10 
0. 14 
0. 10 
Longer diameter of ovum 
0. 025 
0. 026 
0. 026 
Shorter diameter of ovum x . . . 
0. 013 
0. 014 
0. 014 
No 1 is from Merluccius, the measurements made on a living specimen slightly compressed. Nos. 
2 and 3 are from Pollachius, measurements made of specimens mounted in glycerin. 
Among the specimens from the hake were two sizes; the measurements given are from one of the 
larger specimens. A smaller specimen in life had the following dimensions in millimeters: Length 
1.63, breadth of anterior sucker 0.20, breadth of posterior sucker 0.18. longer diameter of ovum 
0.025, shorter diameter 0.013. The appendix was retracted. Another specimen measured 1.92 in 
length, the appendiculate portion measuring 0.35 in length. The bodies of the smaller specimens 
were much contracted and the appendages retracted. Sections of the smaller specimens show that 
the seminal vesicle is dorsal to the acetabulum and situated rather more toward the posterior than 
the anterior border. The prostate is large and lies dorsal and antero-dorsal to the acetabulum. 
Only one large specimen was found among the preserved specimens. It was sectioned, but since 
it had been subjected to pressure during the preliminary examination it was found to be somewhat 
distorted. The seminal vesicle is at the anterior edge of the acetabulum and there is a conspicuous 
prostate behind the pharynx. Sections of the smaller specimens showed that the excretory vessels 
unite in front of the testes, which, as in the specimens from the pollock, are but a short distance back 
of the acetabulum. The branches of the intestine extend into the appendix. After lying in water 
for some time some of these worms lost the sharply serrate margins, which is a characteristic feature, 
due to the regular transverse plications of the cuticle, and in some of the mounted specimens these 
transverse striae no longer appear. 
While examining some of the smaller specimens at the time of collecting, numerous spherical 
masses were seen, which at first were taken to be ova. Further considerations proved them to be con- 
centric in structure and to lie in the excretory vessels. They were observed in other distoma and appear 
to be solid excreta. Search was made for these spherical bodies in sections, and in the excretory 
vessels some were found which appear to be identical, although much smaller. 
While these specimens, which I have identified as I). ocreatum Molin, agree closely with published 
descriptions of that species, especially those of Olssou, there is one point which I have not been able 
to verify with entire satisfaction. The cirrus of D. ocreatum is papillose. The cirrus in the speci- 
mens which I have examined appears to be minutely papillose, but none were seen with satisfactory 
distinctness. The reproductive aperture is at the under side of the mouth. 
The trilobed character of one of the two vitellaria is clearly shown, and the size of the ova is 
substantially the same in all. At the same time sufficient diversity is shown in these several varieties 
to make it desirable that those forms belonging to the subgenus Apoblema, which have equal or nearly 
equal suckers, be revised with care. 
