THE ANNELIDA AND SCOLEC1DA. 127 



tinguished by the presence of a suture dividing its median from 

 its lateral regions. 



The ANNELIDA are primarily divisible into two groups the 

 Chtetophora and the Discophora. The former has probably 

 more than a merely ordinal value. 



1. The CH^TOPHORA have chitinous setfe developed in sacs 

 of the integument. These are sometimes merely implanted 

 in the walls of the somites, at others, they are borne by distinct 

 rudiments of limbs, or parapodia. They never possess sucker- 

 like organs of adhesion. 



The Errantia and Tubicola, the Earthworms, and the 

 Gephyrea form this division. 



2. The DISCOPHORA (or Leeches) never possess parapodia 

 nor lateral series of setse occupying their place, but they are 

 provided with one or more sucking disks. 



V. THE ANNULOIDA. 



The groups comprehended under the title of the SCOLECIDA 

 are probably of greater importance than orders, but for the 

 present I shall take them as such. 



1. The TREMATODA (or Flukes) possess an alimentary canal, 

 but are always devoid of an anus, and are usually provided with 

 one or more suckers for adhesion to the animals in, or on, which 

 they are parasitic. The body is not covered with cilia in the 

 adult state, nor is it segmented. There is only one set of 

 sexual organs usually hermaphrodite. The larvae are often 

 tailed or cercariform never provided with three pair of 

 hooks. The species have asexual conditions, but are never 

 " cystic." 



2. The T^NIADA (or Tape Worms and Bladder Worms) 

 possess no alimentary canal. The anterior end of the body is 

 provided with suckers, hooks, or foliaceous appendages, or with a 

 combination of all three. The hermaphrodite reproductive 

 organs are serially repeated, many times, in the body. The 

 larvas are oval, and provided with three pairs of hooks, arranged 

 in bilateral symmetry. Beside the <: cestoid" sexual forms, 



