602 THE ANIMAL KINGDOM. 



( = Pherusidae\z.g. Siphonostoma, in Spirogr aphis Spallanzanii( Sabclla 

 ventilabruni), and in many Serpulinae, owing to the presence of a respira- 

 tory pigment, chlorocruorin, capable of oxygenation and de-oxygenation. 

 Colourless corpuscles of fixed outline are found in the fluid (most Oligo- 

 cJiaeta, several Polychaeta, \. e. Eunice, Stauroccphalus, Nereis, Syllidae, 

 Ophelia, Cirrhatulus\ pinkish corpuscles in Magelona (Mclntosh). Special 

 corpuscles tinted with haemoglobin are met with in the coelomic fluid of the 

 anangian Glycera and Capitella, and red-coloured corpuscles occur similarly 

 in Heteroterebella sanguinea which possesses a pseud-haemal system (Clapa- 

 rede). Amoeboid corpuscles are always present in the coelome. 



Respiration is carried on partly by integumental capillaries, when 

 present, and in many Polychaeta by branchiae (p. 595). 



The excretory organs or nephridia occur as a rule one pair in each 

 somite, but they are generally aborted in the anterior region of the body, 

 especially when there is a muscular pharynx. Their number is much 

 reduced in some Tubicola, e. g. to eight pairs in Terebella gigantea, six pairs 

 in Arenicola, and they are therefore present in certain somites only which 

 may be anterior as in the two genera just named, or median and posterior 

 as in Chaetopterus, Sabella, Myxicola. Each organ consists essentially of a 

 ciliated tube terminating internally in a ciliated and generally funnel- 

 shaped orifice, and opening externally by a nephridiopore. This pore 

 varies in position. It is in most Oligochaeta near the ventral bundle of 

 setae (see p. 205) ; near the parapodium in Polychaeta, either ventral to it, 

 e.g. in Polynoe, or dorsal, e.g. Sthenelais, Notomastus, or in front of it 

 The section of the tube contiguous to the pore may be wider in calibre as 

 in Lumbrictis and its allies, or vesicular as in aquatic Oligochaeta and some 

 Tubicola, and in both cases is provided with a muscular coat 1 . The vesicle 

 may have a glandular epithelium. It may be the only persistent part of 



1 Cosmovici's account of the nephridia in Polychaeta is followed in the text. He applies the 

 term ' organ of Bojanus ' to the vesicle, and that of ' segmental organ ' to the ciliated tube. The 

 vesicle is probably formed by invagination of the hypodermis, as Vejdowsky has found it to be in 

 aquatic Oligochaeta. The presence of the vesicle in some somites, its absence in others, in one and 

 the same animal, e. g. Ophelia, is a remarkable fact. A pair of vesicles, very large in size, opening 

 on the head in Serpulidae, was supposed by Claparede to secrete the material for the tube. That 

 author figures a stream of mucus passing out of the branchial funnel of Myxicola. See Supplement 

 aux Annelides Chetopodes du Golfe cle Naples in Mem. de la Soc. de physique et d'histoire Nat. de 

 Geneve, xx. 1869, p. 512, PI. xiv. Fig. 2. The position of the apertures (double, according to 

 Cosmovici, single, according to Claparede) in this animal and in other Serpulidae is noteworthy. See 

 note, p. 596, ante. 



Cosmovici points out that the nephridial funnel opens into the median chamber of the coelome 

 containing the digestive tract in all Krrantia and in those Tubicola which are distinctly segmented. 

 It opens in other Tubicola, e. g. Arenicola, into the lateral coelomic chambers (p. 597). The 

 nephridium itself is usually applied in the Errantia to the posterior face of a septum ; sometimes to 

 the anterior face as in Cirrhatulus. For a good figure of the nephridium and its papillate external 

 pore in Polynoe clava, see A. G. Bourne, Tr. L. S. ii. PI. xxxvi. Fig. 22. The pores are papillate also 

 in Notomastns {Capitellidae}. 



