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 

 lopment 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- , Transvers f s ? c ''. on . f Leech; * v , 



dorsal vessel ; i, digestive canal ; m, 



nective tissue, the suckers *S^J^Z t ^ 

 chiefly consist. There is rarely ch >' ma ' /z/ lattral vcssel - 

 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, 

 twi-nty-one in Clepsine, 



idclot}. In the young 

 these are two lateral cords, 

 which remain apart in i\Ia- 

 lacobdella [Fig. 27,0), but 

 imate and often fuse 

 in othTs. The anterior and 



inirlia an- the 



, and an- knotted ; 



four 1 anteriorly in 



n in I lirudo ; 



iorly in ( lep- ' 



J ' 



sine. Above tin- pharyn , 



