CHAPTEE XIY 



HIKUDINEA (LEECHES) 



INTRODUCTION ANATOMY REPRODUCTION CLASSIFICATION- 



RHYNCHOBDELLAE AND GNATHOBDELLAE 



" The external appearance of the Hirudinea," remarks Professor 

 Vaillant, 1 " permits us, save for rare exceptions, to recognise at 

 once the animals which belong to that group." The leeches are 

 distinguished as a rule by the possession of two suckers, one at 

 each end of the body ; their general shape usually differs from 

 that of other Annelids by its oval contour and its dorso- ventral 

 flattening. Cyclicobdella lumbricoides of Grube, which Blanchard 

 has stated to be the same species as Nephelis tergestina, has, 

 however, almost the form of an earthworm by reason of its 

 cylindrical shape and the inconspicuousness of the suckers, while 

 Lumbricobdella also resembles an earthworm and has no posterior 

 sucker at all. 2 The Oligochaet family Discodrilidae (see p. 376) 

 agree with the leeches in their parasitism, in their general shape, 

 in the presence of two suckers, and, furthermore, in the existence 

 of jaws, which are found in no other Oligochaet, but occur in a 

 large number of the Hirudinea. These facts, indeed, though not 

 perhaps important by themselves, are indications of the really close 

 resemblance of the Hirudinea to the Oligochaeta, a group which 

 they approach not merely in such habits as the formation of a 

 cocoon in which the eggs are enclosed, but also in many important 

 points of internal and external structure. Indeed, the fundamental 

 differences between the two groups are not numerous, and are not 

 of such importance as has been given them by some writers. 

 Leeches are to be found in most parts of the world, in situa- 



1 " Anneles," vol. iii. 1889-90, p. 477, in the Suites a Buffon. 

 - See v. Kennel, Zool. Jahrb. ii. 1887, p. 37. 



