24 Catalogue of Chaetopoda 



principle of classification was maintained, especially during the twenty 

 years subsequent to its enunciation, by a number of writers who 

 placed the family Telethusae in an order designated Dorsibranches, 

 Notobranchia or Mesobranches. 



II. Savigny (1820) divided marine worms, according to the charac- 

 ters of the chaetae, head and proboscis, into two orders Nereideae 

 and Serpuleae, to the latter of which the family Telethusae was 

 referred. The principles of classification laid down by Savigny were 

 adopted and extended by later workers, few of whom, however 

 retained the original ordinal names. 



III. Orders of similar constitution to those of Savigny were pro- 

 posed by Lamarck (1818) and named Antenne'es and Sedentaires, 

 and by Audouin and Edwards (1832), who separated the Errantes 

 from the Sedentaires by their mode of life. This classification was 

 adopted by Quatrefages (1865), and the ordinal names Errantia and 

 Sedentaria were in general use during the next thirty years. Audouin 

 and Edwards placed Arenicola in the order Errantes, but Lamarck, 

 Quatrefages and most other writers have referred it to the Sedentaria. 



IV. Grube (1850) used the mode of feeding, and certain mor- 

 phological characters, as a means of separating the Polychaeta into 

 two sub-orders Eapacia and Limivora, to the latter of which 

 Arenicola was referred. This system of classification was adopted by 

 Johnston (1865) and others. 



V. The systems of Profs. Benham and Hatschek are based on 

 anatomical characters, and divide the Polychaeta into six or seven 

 sub-orders. The family Arenicolidae is placed in the sub-order 

 Scoleciformia (Benham), which is similar to the sub-order Drilo- 

 morpha (Hatschek), the chief features of which may be stated thus 

 the prostomium 1 seldom bears sensory processes, the peristomium 2 has 

 no cirri, the parapodia 3 are feebly developed and may be absent, cirri 4 

 are usually wanting, true uncini 5 are not present, the buccal region 

 and pharynx are eversible and there are no jaws, some or many of 

 the septa are wanting, and the nephridia are reduced to a compara- 

 tively few pairs, which are all alike. 



1 The anterior portion of the head, namely, that part which is pre-oral ; 

 equivalent to the " head-lobe," or " Kopflappen " (Grube) of some earlier writers. 

 The posterior portion of the head, immediately following the prostomium, 

 and bearing the mouth. 



3 Paired, unjointed, lateral outgrowths of the body wall in each body- 

 segment, bearing chaetae and serving as organs of locomotion. 



4 Filamentous sensory processes. 



5 Chaetae in the form of short and sharply curved hooks, characteristic 

 especially of Terebelliformia and Sabelliformia. 



