174 MR W. E. HOYLE ON 



to be inserted pinnately into a tendon which is attached to the dorsal angle of 

 the hook. 



The Flexor unci (fig. 12, u.f) is inserted into the opposite angle of the hook, 

 and arises, as Leuckart has well described, from the basal joint of the hook, its 

 fibres crossing those of the muscle last mentioned. 



The Flexor accessories unci (fig. 12, u.f. a) is a long thin band which appears 

 to arise in the mesoblastic tissue of the body, and passes forwards approaching 

 the flexor unci on its ventral aspect at a slight angle, and is inserted close 

 beside it. 



The Retractor unci (fig. 12, u.r) passes forwards and slightly towards the 

 dorsal surface, and is inserted close to the two last. It acts to some extent as a 

 flexor, but in conjunction with other muscles, more particularly the extensor, it 

 produces that movement of retraction of the hook as a whole which Leuckart 

 has described as occurring in the living Pentastomum, but which unfortunately 

 I have not had the opportunity of witnessing. 



In addition to these four muscles are two attached to the extremity of the 

 basal joint of the hook. 



The Protractor basis unci, arises from the anterior surface of the head, and 

 passes backwards to be inserted into the posterior extremity of the basal joint 

 of the hook. It consists generally of more than one slender bundle, and its 

 action can be readily inferred from an inspection of the drawing (fig. 12, u.b.p). 



The Adductor basis unci (if it be allowed to use the word in the sense of 

 drawing towards the ventral surface) is inserted along with the last named, but 

 its fibres pass inwards from an origin near the ventral surface of the body 

 cavity (fig. 12, u.b.a). 



In addition to the definite muscular bundles above described, a set of fibres 

 arises from the cuticle all round the invagination in which the hook is situated; 

 these muscles, which may be termed " retractors of the cuticle," are obviously 

 charged with the function of facilitating the egress of the point of the hook 

 from its sac and increasing the extent of its protrusion. 



The Digestive Tract. 



This portion of the animal's anatomy consists only of four well-defined 

 portions — 



1. The Oral Papilla. 



2. The (Esophagus. 



3. The Stomach. 



4. The Rectum. 



1. The Oral Papilla. — In the description of the outside of the animal, men- 

 tion has been made of a small circle lying between the two pairs of hooks. 



