A CATALOGUE 



BRITISH NON-PARASITICAL WORMS. 



1 HE Helmintha or Worms are invertebrate soft animals, symmetri- 

 cally bilateral, or with the viscera arranged on the sides of a lon- 

 gitudinal axis. They are never organically attached to foreign 

 bodies or their own cases, and are capable of progression to a more 

 or less extent. They move forwards, some by a continuous gliding, 

 some by a succession of trails, some by undulations in the water, and 

 others by means of soft appendages and bristles placed along the 

 sides. Diesing's definition of the class is as follows: — "Animalia 

 evertebrata, inarticulata (^. e. extremitatibus articulatis nuUis prse- 

 dita), nunc mollia aut elastica, ebranchiata, setis retractilibus nullis 

 (Achsethelmintha) ; nunc mollia, ebranchiata v. branchiis externis 

 munita, setis retractilibus instructa (Chsethelmintha)." 



There are two kinds of Worms, — one which are found within the 

 viscera of living animals, and which cannot maintain their existence 

 in any other situation ; and another which lead an exterior life, 

 either entirely independent, or as the external parasites of some 

 aquatic animals. These, however, the parasites can forsake at will, 

 without incurring the penalty of death. It is the second kind of 

 Worms to which this Catalogue is restricted ; and they may be con- 

 veniently included in the following Orders : — 



A. Apodous : the body without bristles on the sides. = Apoda, 

 Macleay. = Achaethelmintha, Diesing. 



* Body exannular. 

 I. Order. TURBELLARIA. The extremities of the body simple 

 and continuous with it : no distinct head. 



