458 ANNELIDA. 



the main group, a similar position to that assigned above to Neomenia 

 and Chaetoderma in the Molluscan phylum. They are isolated forms 

 with Annelidan affinities. As to Saccocirrus it seems clear that it 

 connects Archiannelids with such Polychaets as the Opheliidae, in 

 which, though coelomic septa are absent, the oblique septa, predomin- 

 ance of the longitudinal muscles and in Polyophthalmus at least, if 

 not in other genera, the cephalic ciliated pits, and contiguity of the 

 ventral nerve cords to the ectoderm are noticeable characters. 



Class 2. CHAETOPODA. 



Annelids with conspicuous setae. TJie perivisceral cavity is in 

 many cases divided by septa. 



The Chaetopoda include Polychaeta, in which the setae are 

 generally borne on parapodial processes of the body, which may be 

 fairly compared to the appendages of Arthropods, and the OUyochaeta, 

 in which there are no parapodia, the setae simply projecting from 

 the body-wall. 



Order 1. POLYCHAETA.* 



Marine Chaetopoda with numerous setae embedded in parapodia; 

 usually icith distinct head, tentacles, cirri and branchiae. They are 

 for the most part dioecious, and develop with a metamorphosis. 



The Polychaeta are, with a few exceptions, marine Chaetopods, 

 in which the setae are numerous and borne upon special processes of 

 the body-wall called parapodia. The head, which is called the 

 prestomium, very generally bears tentacular appendages, while the 

 next segment, called the peristomium, is usually modified and may 

 be fused with one or two of the following segments. The alimentary 

 canal generally possesses an eversible buccal region, and a muscular 

 protrusible (not eversible) pharynx. The coelomic septa may persist, 



* Audouin et Milne -Edwards, Ann. Sci. Nat., t. 27-30, 1832-38. Delle 

 Chiaje, " Dcscrizione e notomia degli animali sensa vertebre d. Sicilia citeriore," 

 Napoli, 1841. Quatref'ages, " Histoire Nat. d. Anneles," 1 and 2, 1865. Ed. 

 Claparede, " Annelides Chetopodes du Golf tie Naples," 1868, and Supplement, 

 1870. Ehlers, "Die Borstenwurmer," 1868. Johnston, "Brit. Mus. Catalogue, 

 of non-parasitical worms," 1865. Mclntosh, "British Annelida," Trans. Zoo/, 

 tioc., ix., 1877. Malmgren, " N ordiska Hafs-Annulater," Ofversicjt k. Vet. ATcad. 

 FordhandJingar, 1865 and 1867. St. Joseph, "Ann. Polychetes des cotes de 

 Dinard," Ann. Sci. Nat. (7), 1, 5, 17, 20, 1886-94. Malaquin, Rccherchcs sur 

 les Syllidiens, 1893. Bobretzky et Marion, " Et. s. les Annelides du Golf de 

 Marseille, Ann. Sci. Nat. (6), 2, 1875. Mclntosh, "Report on the Annelida 

 Polychaeta," Challenger JtejMrts, 1885, and numerous papers by E. Grube. 

 W. B. Benhani, "Polychaeta," Cambridge Natural History, 1896. Meyer. 

 "Stud. lib. d. Kurperbau der Anneliden," Naples Mitth., 7 and 8, 18S7-8. 

 Pruvot, Arch. Zool. Exptr. (2), 3, 1885. 



