FISH PARASITES COLLECTED AT WOODS HOLE. 

 The following table gives the dimensions in millimeters : 



293 



No. 1 was a living specimen, slightly compressed; Nos. 2 and 3 were mounted in balsam. A 

 specimen free in sea water measured 0.3(5 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 0.16 0.45 



P.readth 0.26 0.17 0.21 0.11 0.14 0.09 0.10 0.17 



Sections were made of some of the pyloric c;eca and revealed numerous distoma embedded in the 

 contents of the cseca (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 these 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 the seminal vesicle and prostate were relatively large. 

 The genital aperture is in front of the acetabulum and apparently near it. The ova are 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 these distoma in a single host. In the first 

 instance the pyloric creca were seen to bo minutely punctured with dark specks. When they were 

 placed in a small dish of sea water and examined with a hand lens, immense numbers of small distoma 

 were seen on the pyloric ca^ca. The sketch of a part of a section of the pyloric c;pca (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 ca>ca, it may be inferred that the vitality of the host is affected seriously by their 

 presence. 



Distomum areolatum Rudolphi. 



[Plate 39, figs. 60-63, TJ. S. N. M. No. 6517.] 



Some small distoma, found in a dish in which viscera of the white perch (l\foroi>c americana) had 

 been lying, are referred, not without some doubtj to this species. The following description is based 

 on a mounted specimen. Body covered with short, fiat spines, which appear slender 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, subtcrminal 

 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. G^sophagus 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. Tostes, two rather large bodies placed side 

 by side on opposite sides of the median line, with their anterior borders abont the middle of the body. 

 The cirrus pouch lies back of the acetabulum and to the right. 



