82 Part [I] —Twenty-sixth Annual Report 
rack and Oresund * and Johnston from similar Dog-fishes and from Thorn- 
back Skates, trawled in the Irish Sea.t 
Tetrarhynchus minutus, P. J. van Beneden. PI. V., figs. 7-8. 
1850. Tetrarhynchus minutus, van Ben., Les Vers Cestodes, 
p. 40m Plo 
This Cestode was obtained in the intestine of an Angel-fish, Sqwatina 
angelus, captured in the Firth of Clyde in May 1904; it is a smal! species 
aud easily overlooked. As indicated above, this species was described by 
van Beneden in 1850, and the characters by which he distinguishes it are 
as follows :—“ Les bothridies ne sont pas complétement separées les unes 
des autres ; les trompes sont couvertes de crochets recourbés ; les gaines 
des trompes formeut des tours de spire; les segments sont tres-longs et peu 
nombreux,” and he adds that the species may be recognised from closely- 
allied forms by its small size, the length of the segments, which are several 
times longer than broad, and the number of articulations, which seldom 
exceed six, the last segment being already mature when five or six rings 
can be counted, whereas in other species mature segments do not usually 
occur till a larger number of rings have beea formed. Van Beneden’s 
specimens of 7. mtnutus were also obtained from Squatina angelus, 
which appears to be the only kind of fish this Cestode has been recorded 
from. 
Another species of -Tetrarhynchus—T’. erinaceus, P. J. Van Beneden, 
described in 1858,+ has been noticed in fishes examined at the Labora- 
tory, usually in small cysts on the walls of the stomach, and pyloric czeca 
of Gadoids (Cod-fishes and Saithe). 7’. erinaceus, in this encysted state, 
according to van Beneden, is unable to attain sexual maturity, and is 
therefore placed by him among the zenosites or strangers—parasites that 
have not yet reached their ultimate destination, or, as that author remarks, 
“‘Ce sont des parasites en transit.” The encysted 7etrarhynchus can only 
reach the sexually mature stage after it has been transferred to the 
stomach of some Plagiostome, and the fish belonging to that group in 
which the parasite has been most frequently observed in a sexually 
mature condition is the Thornback Skate, Raiu clavata. The proboscides 
do not appear to be exserted while the parasite remains within its cyst, 
but when removed from it and placed in a little sea-water the Cestode, 
apparently recognising the change in its environment, soon begins to push 
out its formidably armed proboscides. So far as I have observed, the 
thrusting out of these armed appendages is not completed by a continuous 
movement, but intermittently, as if the operation were a work of some 
difficulty, and that a pause was necessary for further effort. I have also 
observed that, though the fish may have been dead for a good while, the 
encysted parasite would be still alive, and on being removed from its 
prison would in a shor$ time begin to thrust out its proboscides. 
T. erinaceus is a widely-distributed species, either in its encysted state or 
in its state of sexual-maturity, for it has been recorded not only by van 
Beneden, Olsson, and other European Helminthologists, but also by Linton 
in his papers on the Entozoa of American fishes. 
Two of the species of Tetrarhynchus mentioned here—T. tetrabothrius 
and 7’. minutus—have also been assigned to the genus Rhynchobothrium, 
Rudolphi, but meanwhile I leave them where van Beneden placed them. 
*Bidrag till Scandinaviens fauna, Kongl. Sv. vet. Akad. Handl., Bd. 25, 
No. 12, p. 25 (1893). 
+ Rept. for 1905 of the Lancashire Sea Fisheries Laboratory, p. 174 (1906). 
+ Mem. sur les Vers intestineaux, p. 128, Pl. XVIII. 
