436 ALFRED GIBBS BOURNE. 



alimentary canal have been termed dorsal-ventral fibres, while 

 the lateral series are termed radial (figs. 9 — 14, 61 — 64, 

 m. rad.). They occur in all the genera. They form bundles 

 of fibres which spread out at either extremity, the out-spreading 

 fibres, which are to a large extent formed as branches of the 

 fibres forming the bundle, run through the circular layers oi 

 muscle and only terminate close underneath the epidermis 

 (fig. 9, m. rad.). The two central rows of bundles pass be- 

 tween the csecal dilatations of the oesophageal portion (see 

 infra, Al. Canal) of the alimentary tract in those genera 

 where such exist. 



Leuckart^ points out that these dorso-ventral muscles separate 

 the leech-body into longitudinal chambers containing alimen- 

 tary canal and nerve-cord, generative organs, lateral blood- 

 vessels, and bundles of muscular fibres respectively ; they are 

 not, however, arranged as walls running longitudinally but as a 

 series of isolated bundles, and it seems more important to note 

 their metameric repetition in series in correspondence with 

 the metameric segmentation of the other organs. Lang has 

 noted this arrangement.- They represent the diaphragmatic 

 septa of the Chsetopoda. In the region of the pharynx (fig. 16, 

 m. rad.) in the Gnathobdellidse they acquire a special con- 

 nection with its wall and help in suction (see Pharyngeal 

 Muscles). 



Muscles in the Wall of the Alimentary Canal. — 

 These are extensively developed in the region of the pharynx 

 only (figs. 16 — 24). If we compare the proboscis of the Rhyn- 

 cobdellidse, not with the pharynx alone of the Gnathobdellidse, 

 but with the whole body in that region, we find a striking 

 similarity between the two in the arrangement of the muscular 

 and other elements. 



The proboscis of the Rhyncobdellidse is merely the anterior 

 portion of the body which has taken on a special development, 

 and can be withdrawn into a proboscidian sheath ; this latter 



' ' Die Menschliclieu Parasiten,' p. 645. 



2 « Neapel. Zool. Stat. Mittlin," 1882, 'Der Bau von Guuda Segmen- 

 tata;' also ' Archiv de Biologic,' 1881, p. 558. 



