18 



LEECHES 



Pigment cell Cuticle Epidermis Pearshaped gland 



Dermis ^-—-^^z 

 Circular 

 muscles 



Oblique 

 muscles 



Botryoi 

 tissue 



I m m 



Blood 

 capi I lary 



Tubular 

 gland 



Longitudinal 

 muscles 



Connective 

 tissue 



Dorso - ventral 

 muscle 



Fig. 9. 



Details of the tissues found between the gut and the 

 cuticle in a transverse section of Hirudo. 



the formation of the cocoon. The first are the chitogenous glands 

 which secrete the outer casing. These lie among the circular 

 muscles. The others are the albumen glands, which lie deeper, 

 among the longitudinal muscles. The sense organs of the epidermis 

 show several grades of complexity from simple nerve endings to 

 well differentiated eyes (Fig. 10). The details of these are discussed 

 in connexion with the physiology of the nervous system, p. 79. 



Dermis 



Between the epidermis and the muscle layers is a zone of fibrous 

 connective tissue. It consists of a ground-substance containing a 

 high concentration of acid muco-polysaccharide, and interlacing 

 connective tissue fibres. Bradbury (1958) has shown that the 

 fibres consist of a cortex which is probably collagenous and a 

 medulla which is an extension of the cell body of the fibrocyte. 

 He suggests that the collagen fibres are produced at the surface 

 of the fibrocytes. Pigment cells (brown, black, and green) are also 

 present in this zone. As has been mentioned above, the epidermal 

 gland cells penetrate into the dermis, and in highly glandular 

 regions may leave little room for connective tissue. 



