422 Mr. H. A. Baylis on a remarkable 
other at the invagination. Thus the neck is lined by a thin 
euticle, which is followed by two layers of muscles—the inner 
coat circular, the outer longitudinal. Outside the longitu- 
dinal muscles there is a coat of parenchymatous tissue, with 
very densely crowded nuclei on the inner side. The outer 
boundary of this layer, like the inner boundary of the wall of 
the bladder, is vaguely defined, and the parenchyme-cells 
seem to be bathed in the fluid contained in the bladder, 
which in the fixed material has become coagulated into a 
flocculent mass, containing numerous retringent granules, 
SYSTEMATIC POSITION. 
The structure of the scolex enables the affinities of this 
larval form to be decided with some precision. It may be 
assigned definitely to the genus Monorygma, Diesing, 1863, 
of the family Phyllobothriide. The question therefore arises 
whether it can be specifically determined. ‘The worms of 
this genus, of which six species appear to have been described 
up to the present, are all parasitic, in their sexual stage, in 
sharks and dogfish. 
The six known species are the following :— 
1. M. perfectum (van Beneden, 1853) [Anthobothrium per- 
fectum}). 
Host: Lemargus borealis. 
2. M. gracile (Olsson, 1869) [ Trilocularia gracilis]. 
Host: Acanthzas vulgaris. 
3. M. elegans, Monticelli, 1890 [originally described by 
Zschokke, 1889, under the name of Monorygma per- 
fectum, Diesing }. 
Hosts: Seyllium catulus and S. stellare. 
4. M. chlamydoselachi, Lonnberg, 1898. 
Host: Chlamydoselachus anguineus. 
3. M. dentatum, v. Linstow, 1907. 
Host: a shark (Antarctic) of unknown determination. 
6. M. rotundum, Klaptoez, 1907. 
Host: Notidanus | Hexanchus] griseus. 
