408 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
the subject-matter under the several hosts has greatly facilitated this plan. In all 
cases, where not explicitly stated to lie otherwise, the food notes state the food as it 
was actually found in the Woods Hole fishes. 
Analytical keys for the determination of genera of cestodes and species oi 
distomes mentioned in this paper have been introduced. For the determination of 
monogenetic trematodes recourse may be had to Pratt’s Synopsis of the Heterocotylea 
(American Naturalist, vol. xxxiv, pp. 645-662). 
But few changes have been made in the nomenclature adopted in former papers, 
although this is not because the author is entirely satisfied with the old. The cestode 
originally called Orygmatdbotlirium angustvni has been referred in this paper to 
the genus Grossohotlirium. Following the nomenclature of Pratt’s excellent synopsis, 
Octobotbfriwn denticulatvm becomes Dactyl ocotyle denticulatuvi , Ootoplectanum affine 
becomes Did lidophora afr.nis, Wiizschia elegans becomes JV. elongata , and Tristommn 
rudolpliwmum becomes T. moke. 
The generic name Distomum is retained, as it is sufficiently definite for the 
purposes of this paper. During the past summer the author has been much 
impressed by the variety of shapes which the same species of distome may assume, 
even when it is under the same conditions. When variations in conditions are made, 
as, for example, when some are placed in fresh water, other’s in sea water, others in 
normal salt solution, or when they are killed under pressure with application of 
heat, or when different killing fluids are used; further, when differences in age of 
specimens are considered, as affecting the occurrence of spines on the body or around 
the mouth, or the relative proportions and even disposition of the reproductive 
organs, the variety of forms to be found in the same species is very great. The 
variation in proportions of the muscular suckers, even, is often considerable among 
the individuals of the same species, and the ova, while furnishing a valuable criterion 
of species, frequently vary in the same species and even in the same individual. 
The explanation of the wide distribution of such a form as the species identified as 
Distomum appendicidatum is doubtless to be found in the nature of the intermediate 
host or hosts. Pratt 1 describes an immature appendiculate distome which he finds 
in copepods, which, without much doubt, is the young of this species. Since copepods 
furnish the principal food of the majority of the young of the food-fishes, it is easy 
to understand how the latter became infected. It is to be noted further that most of 
the fish in which this distome was found were young. 
While this report concerns itself principally with helminth entozoa, a few 
ectoparasites, both helminths and copepods, and a few sporozoa are noted. Some 
deep-water fishes are included which do not belong to the Woods Hole fauna. 
Notes on the nematodes, which have been collected by or for the author at 
Woods Hole, are given, together with notes on nematodes which were found in a 
collection of entozoa belonging to the United States National Museum, the cestodes 
and trematodes of which were reported on in vols. xxx and xx of the Proceedings 
of the National Museum (Nos. 4, t *5, and <5, p. 424). The great majority of these 
nematodes are immature and no attempt has been made to give them specific names. 
A few adult forms, with sufficiently conspicuous characteristics, have been described 
as new species. These will be found in the alphabetic list of nematodes (p. 410-411). 
iA Contribution to the Life-history and Anatomy of the Appendiculate Distomes, Zoolog. Jahrb. xi, 1S93. 
