THE ALIMENTARY CANAL. 63 



which encircle the body transversely. The layer 

 itself is not much thicker than the epidermis, but 

 the transverse muscles of the dermis should, per- 

 haps, be grouped with it. 



2. The middle or oblique layer of muscles is -more deeply 



placed, and is separated from the circular layer by 

 a stratum of connective tissue. The fibres run 

 obliquely round the body. 



3. The inner or longitudinal layer of muscles lies im- 



mediately within the oblique layer, and is by far the 

 thickest of the three layers. 



4. The dorso-ventral muscles are bundles of muscle-fibres 



crossing the body more or less obliquely from the 

 dorsal to the ventral surface. They pass between 

 the bundles of longitudinal muscles and through the 

 oblique and circular layers, their ends spreading out 

 just beneath the epidermis. 



D. The Alimentary Canal. 



A section across the middle portion of the body will cut the 

 crop, of which the median portion and the lateral diverticula 

 will in most sections appear separate from each other. 



The walls consist of an outer connective-tissue layer with 

 a few muscular fibres, and an inner lining formed of a single 

 layer of short columnar epithelial cells. The folds into which 

 the inner surface is thrown involve the connective-tissue layer 

 as well as the epithelium. 



E. The Lateral Tubes and Sinuses. 



The blood-spaces and lateral tubes correspond to the 

 body-cavity of higher animals. They are readily recog- 

 nised in sections, owing to the deeply staining clotted blood 

 with which they are filled. 



1. The dorsal and ventral sinuses he in the median plane, 

 above and below the crop respectively. They have 

 thin non-muscular walls, and the ventral one encloses 

 the nerve-chain. 



