§ 158. THE ANNELIDES. 171 



These last are sometimes found alone. <'"^ With many of these An- 

 nclides, the transverse vessels are dilated, before branching, into real 

 branchial hearts.*'''' As their branchiae are variously situated among the 

 transverse anastomoses, the distinction between the arterial and venous 

 blood is not as marked as with the Capitibranchiati ; it must be arbitrary, 

 as with the Hirudinei and Abranchiati. The blood is usually red, but 

 sometimes is yellow or nearly colorless.*^' 



CHAPTER VII, 



KESPIRATORY SYSTEM. 



§ 158. 



With the various families of the Aunelides, the respiratory organs are 

 formed after wholly dissimilar types. 



AVith the N emertini, they are least developed, for, excepting two longitu- 

 dinal fossae upon the sides of the cephalic extremity,*'* there are no organs 

 which cau be regarded as of this nature. 



These two respiratory cavities are of variable depth, and their lateral 

 borders are so approximated as to have the aspect of a longitudinaropen- 

 ing, and with some they are situated so far out on the cephalic extremity as 

 to be blended together. *-> They are lined with a delicate ciliated epithe- 

 lium, quite different from that covering the rest of the body,*"' and by the 

 vortex actions of which, fresh water is brought constantly in connection 

 with the blood. *^' Considering the smallness of these organs, it is very 

 probable that the whole skin has also a respiratory function. 



i^ Arenicola ; see Milne Edwards, Inc. cit. PI. Micrura fasciolata {Ehrenber^, Symb. phys. 



XIII. I'iiyto/.oa tab. IV. fig. 4. e. i. g.). 



lii Eunice ; Ibid. PI. XII. fig- 2. H See QuatrefTs;es, Resne anira. illustr. Zooph. 



■-'0 With Eunice, Nephtys,Glyr.era, anil Areni- PI. XXXIV. fig. 1, b. b. {Neinertes Camillae). 



cola, the blood is red ; with Phyllodoce, it is yel- 4 Ratlikc (see above, § 149, note 1) is of the opin- 



luw ; and it is nearly colorless with Aphrodite, ion that these two cephalic fossae are tlje seat of 



Polynot, and Sigalion ; see Milne Edwards, loc. touch ; but the view of Orsted (Beschreib. d. Platt- 



cit. p. 196.* wiimier, p. IS, 77), who thinks them of a respira- 



1 S3e Mailer, Zool. Danica. Tab. LXVIII. fig. tory nature, is, perhaps, the more correct. Insup- 



1-4 (Tetrasiemma {Planaria) riride) ; Delle port of this last, is the fact of the presence of cili- 



ciiiaje, Memor. loc. cit. Tav. LXXVIII. tig. 8, a ated epithelium, and of a very large blood-vessel 



( Polia seniculata) ; Q'loy and Gai?nard, At\as directly beneath them (see Qiiatrefai^es, loc. cit. 



/o)l. de I' Astrolabe Zooph. PI. XXIV. fig. 10 (Bor- PI. X.X.XIV. fig. 1. g. g. (Nemert'e.i Camillae)) 



lasia viridis) ; and the Diet. d. Se. Nat. LVII. Art. and which, in many Nemertini, is clearly seea 



l^ers, p. 574, PI. Parcntoraozoaires, Nemertes, fig. through the thin epithelium ; see M lie-; Zool. 



1, 2 (Bortasia Ans^liae, and Cerehratulus biline- Dan Tub. LXVIII. (Tetrastemma vivire) ; Delle 



«i!«); also //((.scAAe, Isis, 1830, Taf. VII. fig. 1-3. Cliiaje, Memor. Tav. LXXVIII. fig. 8 (Polia 



Notoxpermus drepanensis. geniculata), and Isis, 1830, Taf. VII. {Notosper- 



- Tetrastemma viiide, Polia geniculata, and mus drepanensis). 



* [ § 157, note 20.] See also for the blood of the Annelidas, Quatrefages, Ann. d. Sc. Nat. XIV. 

 1850, p. 2S7. — Ed. 



