66 
BULLETIN OF THE UNITED STATES FISH COMMISSION 
I agree with Dr. F. Zscliokke {Reclierdies sur V Organisation et la Distribution Zoo- 
logiqne dcs vers Parasites des Poissons D^Eau Douce, 1884), that the generic characters of 
Ligula&re identical with those of Dibothrium. With regard to Donuadieu’s proposed 
union of the different species, to which proposition Zschokke assents, I am not pre- 
pared to express an opinion, iny investigations having been limited to the forms which 
furnish the subject matter of this paper. While the species which I have for con- 
venience named L. catostomi appears to be identical with L. simplicissima, the other, 
Dibothrium cordiceps Leidy, presents some striking differences. 
Although these entozoa are in all probability lai-vm of Dibotliria, the name Ligula 
has been in use so long that I deem it best for the present to retain it for the sucker 
parasite as a designation of this particular form of Dibothrium larva. 
Ligula catostomi. 
[PI. XXIII, Figs. 1-5 ; PL XXIV, Figs. 1-G; PL XXY, Fig. 1.] 
(Dibothrium ligula Domiadieu?) 
Ligula simplicissima RudolpLi. 
Ligula monogramma Creplin. 
Upon opening the body of one of the infested suckers the cavity is found to be 
almost completely filled with the contained parasite or parasites (plate XXIII, fig. 1). 
The presence of the parasite is indicated before the body is opened by the somewhat 
swollen condition of the abdomen. In some cases the abdominal cavity was found to 
be so packed with these worms that the heart, stomach, liver, and spleen were crowded 
into a very small siiace in the antero-dorsal part of the cavity, while the intestine was 
intertwined with the body or bodies of the parasites. 
The parasites are not covered by any special cyst or membrane, but lie free in the 
body cavity. Usually but a single worm occurs in the host, but in one instance three 
were found in the abflominal cavity of a single sucker. The specimens, while present- 
ing some differences in size, agree in their general form and outline, as well as in the de- 
tails of their very simple superficial structure. They all evidently belong to the same 
species. On account of the extreme simplicity of structure, however, it is very diffi- 
cult to determine their exact specific relation to European forms. Since the Ligula; 
attain their sexually mature state in the intestines of certain piscivorous birds it fol- 
lows that this species should have a wide geographical distribution. 
The sketches which accompany these notes show sufficiently well the external 
character of this parasite. In general outline they are strap-shaped, attaining their 
greatest breadth a short distance back of the anterior end, from which point they taper 
slightly towards the anterior end, and gradually towards the posterior end. The an 
terior end is usually broad and btnntly rounded ; in one case, however, it was observed 
to be slightly appressed into a short, blunt, snbcylindrical termination (plate XXIII, 
fig. 5). At the extreme anterior tip there is usually a median longitudinal sulcus extend- 
ing back a short distance on each lateral face. This appears, in section, to be the be- 
ginning of the adult bothrial depressions (plate XXIV, fig. 1). From about the anterior 
third or a little forward ot that point, the body tapers slowly but rather uniformly to 
the posterior end, which terminates at last somewhat abruptly in a rather sharp point. 
The surface of the body appears to the naked eye to be s?nooth or nearly so, but with 
the aid of a simifie lens it is seen to be crossed by fine transverse grooves and wrinkles. 
The grooves or strife are shallow and do not divide the body into segments. They 
