Introduction to Animal Morphology. 



199 



Fig. 26. 



only at the mouth and sucker (Piscicola, Branchio- 

 bdella), and a deeper, secreting a chitinous material 

 which constitutes the "cocoons" for the eggs. These 

 are only developed during oviposition. There are 

 three laminae of unstriped muscular fibres, circular, 

 radiating, or sagittal and 

 longitudinal, having a rich 

 development of connective 

 tissue between the fibres. 

 Some of the second set stretch 

 laterally from the dorsal to 

 the ventral surface; of these 



radial fibres, mixed with con- , Transverse section of Leech; dv, 

 ' dorsal vessel ; t, digestive canal ; m, 



nective tissue, the suckers -"/i^l'^-.-g^y^.^i-Vgrn^'A^ 

 chiefly consist. There is rarely chyma; /..uterai vessel. 



a body cavity (Branchiobdella), but such may exist in 

 the embryo, though absent in the adult. 



The nervous system consists of a ventral cord 

 dilated into ganglia at regular intervals (twenty- 

 three in the common leech, 

 twenty-one in Clepsine, 

 Baudelot). In the young 

 these are two lateral cords, 

 which remain apart in Ma- 

 lacobdella (Fig. 27, C), but 

 approximate and often fuse 

 in others. The anterior and 

 posterior ganglia are the 

 largest, and are knotted ; 

 four are fused anteriorly in 



Clepsine : seven in Hirudo ; ,^> generative organ of Leech; g, 

 ■■■ gland ; s, seminal vesicle ; p, penis ; r, 



seven posteriorly in Clep- "^^f'^^^^^l^^Tt^J:, 

 sine. Above the pharynx, Mafacol^deliT.' ^' ''"'™"' '^'''" °^ 



Fig. 2; 



