TAPEWORM PARASITIC IN THE STICKLEBACK. 115 
classification. Riggenbach (20) lists 29 species, of which only 7 
are satisfactorily described. At the present time, it is impossible 
to say with certainty whether La Rue is right in retaining the 
species Tenia filicollis Rud. and 7’. ocellata Rud. The only 
correct part of Rudolphi’s description is that referring to the 
scolex, and since the scolex is very variable, Rudolphi’s species 
cannot be determined with any degree of certainty. The question 
can only remain in abeyance until the publication of La Rue’s 
monograph. 
Tt cannot be said, however, that La Rue is justified in retaining 
the generic name Proteocephalus. As Lithe (16) has shown, this 
name was used by Blainville (4) for a family of Cestodes con- 
taining Caryophylleus, and for that reason should be abandoned 
in favour of tue next oldest name, /chthyotenia. In the same 
paper in which La Rue rejects the name Jchthyotenia, he pro- 
poses the name Monticellia for the genus Tetracotylus Monti., 
Braun (5) and Lithe (16) having shown that the latter name was 
proposed by Filippi to designate a group of immature Trematodes. 
He thus admits the principle upon which Lihe’s objections are 
based. 
Occurrence. 
The specimens studied were collected from the intestines of a 
number of sticklebacks (Gasterostews aculeatws Artedi) taken 
from the Edgbaston Reservoir. The numbers in a single host 
varied from one to twenty-five. Almost every fish in autumn was 
infected with one or more of these parasites, 75 per cent. of which 
were adult’: in winter, the number of infected fish was considerably 
smaller, and adults were rare; while in spring, the proportion 
of adults again increased. Adult specimens were found, how- 
ever, all through the months September to June, but while 
their proportion to young forms was 75 per cent. in the first 
month, it was only 15 per cent. in March. Von Linstow failed 
to find it adult at all in winter, and Zschokke only noticed it 
three times. 
External Characters. 
The length of adult specimens varies from 24 to 33 mm., the 
breadth from 1:0 to 1:2 mm. The head is almost continuous 
with the neck and is only slightly globular except when violently 
contracted (text-fig. 1): in Kraemer’s specimens it was spherical 
and sharply marked off from the neck. Jt is furnished with 
four suckers, two dorsal and two ventral, and at its apex isa fifth, 
which is not very well developed although apparently functional. 
The shape and size of the head and suckers are subject to 
considerable variation. The whole region of the head anterior to 
the suckers can be retracted (Pl. I. fig. 5): or the retracted area 
may even be so large as to include the suckers themselves 
(Pl. I. figs. 4, 6, 7)—in the latter case, they are hidden in a 
deep vertical fissure, and can only be seen by staining, while the 
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