FISH PARASITES COLLECTED AT WOODS HOLE. 293 
The following table gives the dimensions in millimeters: 
Measurements. 
No. 1. 
No. 2. 
No. 3. 
0. 31 
0. 35 
0. 26 
Breadth 
. 19 
.12 
.18 
Length of oral sucker 
.06 
.048 
.052 
Breadth of oral sucker 
.06 
.041 
.052 
Length of acetabulum 
.. 055 
.038 
.048 
Breadth of acetabulum 
.062 
.041 
.052 
Length of pharynx 
.031 
.035 
.038 
Breadth of pharynx 
.031 
.027 
.031 
No. 1 was a living specimen, slightly compressed; Nos. 2 and 3 were mounted in balsam. A 
specimen free in sea water measured 0.36 mm. in length contracted and 0.57 mm. when extended. 
The ova measured 0.055 and 0.031 mm. in the two principal diameters. 
The following measurements of living specimens show the various shapes assumed by these 
worms : 
Length 0. 26 0. 36 0. 33 0. 21 0. 25 0. 34 0. 1G 0. 45 
Breadth 0.26 0.17 0.21 0.11 0.14 0.00 0.10 0.17 
Sections were made of some of the pyloric cseca and revealed numerous distoma embedded in the 
contents of the caeca (fig. 52). Spherical bodies with a> concentric structure were seen lying in the 
excretory vessel. These masses were not of uniform size; the largest measured 0.01 mm. in diameter. 
They appear to be solid excreta. They are much smaller than the ova and moreover are spherical. In 
these sections it was seen that the oral sucker and acetabulum are of substantially the same size. One 
of the larger specimens, which lay in a favorable position, yielded the following measurements (in 
millimeters) of these parts: Diameter of oral sucker, 0.07; of acetabulum, 0.07 ; diameter of pharynx, 
0.04; length of body, 0.35; breadth, 0.24. 
A large portion of the preserved specimens have the anterior end of body inverted. There is thus 
the greatest variety of outline exhibited by those, specimens, long and short oval, sublinear, elliptical, 
and pyriform, the latter in some form or other perhaps predominating. The excretory vessel appears 
to be large and was seen to expand into a spacious posterior area in some instances (fig. 55). In the 
sections the cirrus was seen to be spinous, and tlio seminal vesicle and prostate were relatively large. 
The genital aperture is in front of the acetabulum and apparently near it. The ova aro few, usually 
three or four — in one case six were seen — but as compared with the size of the worm are very large. 
No attempt was made to estimate the numbers of those distoma in a single host. In the first 
instance the pyloric caeca were seen to bo minutely punctured with dark specks. When they wore 
placed in a small dish of sea water and examined with a hand lens, immense numbers of small distoma 
were seen on the pyloric caeca. The sketch of a part of a section of the pyloric casca (fig. 52) gives 
an imperfect idea of the great numbers of these parasites. When it is remembered that this is what 
is shown in a very thin section and that a long series of sections revealed a similar degree of infection 
throughout the caeca, it maybe inferred that the vitality of the host is affected seriously by their 
presence. 
Distomum areolatum Rudolplii. 
[Plato 39, figs. 60-63, U. S. N. M. No. 6517.] 
Some small distoma, found in a dish in which viscera of the white perch ( Morone americana) had 
been lying, are referred, not without some doubt, to this species. The following description is based 
on a mounted specimen. Body covered with short, flat spines, which appear slonder on the margins, 
probably because there seen on edge. The spines become somewhat scattered posteriorly, but with 
care may be traced nearly if not quite to posterior end. The body is depressed, ovate, and broadest 
toward posterior end. The anterior sucker is unarmed, ovate, with circular aperture, subterminal 
and a little larger than the acetabulum. The latter is sessile, broader than long, and situated about 
the anterior fourth of the body. Pharynx oblong, shorter than the oral sucker. (Esophagus very 
short, shorter than pharynx. Branches of the intestine simple, extending nearly to the posterior end. 
Excretory vessel spacious, at posterior end of the body. Testes, two rather large bodies placed side 
by side on opposite sides of the median line, with their anterior borders about the middle of the body. 
The cirrus pouch lies back of the acetabulum and to the right. 
