4S8 ALFRED GIBBS BOURNE. 



of the proboscis, as shown in transverse and longitudinal 

 sections. 



Looking, in the first place, at the anterior portion of the 

 body — i.e. in the pharyngeal region — in the Gnathobdellidse 

 (fig. 16), we find the following structures, and, passing from 

 within outwards, in the following order : 



1. Pharyngeal epithelium, al.ep. The cells are very minute. 



2. Radiating muscles, m. rad., attached to the basement 

 membrane of the epithelium. These pass outwards on all sides 

 through all the other structures, their branched ends abutting 

 upon the epidermic layer. 



3. Circular muscles, m. circ. int. These form a dense and 

 most compact layer surrounding the three ridges formed by 

 the internal portions of the radiating muscle. 



4. Longitudinal muscles, m. long., arranged in bundles 

 separated by connective tissue and by the radial muscles which 

 run through them. Among these occur the sinuses and vessels, 

 salivary glands, and their ducts. 



5. Circular and oblique muscles, m. circ, are arranged in an 

 oblique layer and an outer circular layer. 



6. Skin, subepidermis, epidermis, ep. ; and cuticle, cu. 

 Compare with this the proboscis of the Rhyncobdellidse 



(figs. 17—24) : 



1. Pharyngeal epithelium, al. ep. 



2. Radiating muscles, m. rad. These are larger than among 

 the Gnathobdellidse. They pass outwards, and abut upon the 

 epithelium on the surface. 



3. Circular muscles, m. circ, developed as in the other 

 group. 



4. Longitudinal muscles, m. long. The portions of the 

 radiating muscles in this layer are very large ; the bundles of 

 longitudinal muscles are consequently very small, and as the 

 blood-vessels {cap.), especially in Piscicola and Branchel- 

 lion, are very large in this region, and the ducts of the 

 salivary glands, gl. s. d., numerous, the longitudinal muscles are 

 reduced to a minimum, there being only three or four fibres 

 in the bundle. 



