210 Henry LesLıe OsBorn, 
in the acetabula of the ventral sucker, 1 «, and in the mouth funnel. 
Owing to its thickness it is thrown into wrinkles by the contractions 
of the animal, a longitudinal system appearing when the body is 
thrust forward and a transverse system when it is shortened (Fig. 3). 
It is as usual entirely devoid of cellular elements, and rests directly 
upon the muscular layer of the body wall. The outer portion is 
slightly darker colored than the inner, but there is no line recogniz- 
able between these. At all of the openings of the body the cuticle 
passes in and becomes directly continuous with the epithelium of 
the organ, as will be more fully noted in connection with those 
parts. There are no spines or cuticular hooks of any kind. Certain 
structures in the cuticle which are related to the parenchymatous 
glands and others that are perhaps sensory will be considered later. 
f) Museulature of the Body-wall and Parenchyma. 
Iron-haematoxylin stains the muscle beautifully, by first over- 
staining and then decolorizing, the arrangement of the fibres and 
their structure can be seen to great advantage. By keeping living 
specimens in a weak aqueous solution of methylene blue the muscle 
fibres and the attached cells can be shown. In the body-wall at 
large the usual arrangement prevails. A tangential section (Fig. 11) 
shows the circular, longitudinal and oblique layers in order, the 
fibres never close together. At the excretory and genital openings 
the fibres are altered to serve as sphincters and dilators, by circular 
and radial arrangement. The absence of a distinct oral sucker is 
a trait common to all the members of this family. The mouth 
funnel acts much like one, and is enabled to do so by the fibres 
which cross it from the outer to the inner wall after the manner 
of the radial fibres in a true sucker, they are aided by well 
developed circular and longitudinal fibres in both the outer and 
inner sides of the double wall. But there is no distinct inner organ 
the homologue of the oral sucker of trematodes in general in the 
adult or at any time so far as known in the life-history of Cotylaspis. 
The ventral sucker originates as a single sucker (Fig. 71) like that 
of the Distomes, the acetabula develop by subdivisions which come 
in at a comparatively late date in the ontogeny. The details of 
the structure of the muscular partitions of the sucker are the same 
as those of Aspidogaster, as described by STAFFORD. 
There is a diaphragm, apparently a modification of the muscular 
system of the body-wall, which runs from the junction of the body- 
