^160. 



THE ANNELIDES. 



178 



arranged loops.*''^ With Lumbricus, these aquiferous canals are sur- 

 rounded by a very distinct vascular net-work, which has a botryoidal 

 aspect from its numerous pedunculated, vesicular dilatations which are filled 

 with blood. ''■> 



§ 160. 



With most of the Capitibranchiati, and Dorsibranchiati, the respiratory 

 organs consist of external branchiae, which are very apparent, although 

 having variations in their development. They always consist of lobules or 

 filaments covered with ciliated epithelium, and in which are very con- 

 siderable vessels as branchial arteries and veins.*" The branchiae are 

 here always situated between the venous and arterial systems, so that a 

 portion only of the whole blood is made to pass through the respiratory 

 organs. 



It is possible that the two bundles of tentacles which are found with 

 many Capitibranchiati, as infundibuliform,*-' or spiral'"' tufts, are also res- 

 piratory ; for their vibratory organs not only draw in food, but also pro- 

 duce a constant change of the water. 



Other Capitibranchiati have distinct and exclusively respiratory organs 

 in the cervical region, which are either dendritic,''" or semi-pinnate.*^' 



With the Dorsibranchiati, nearly every segment of the body has branchiae 

 upon both sides of its dorsal surface. These are so simple and rudiment- 

 ary with the Ariceae, and Nereideae, that they consist only of simple lob- 

 ules, exactly resembling the cirri of the feet.*' 



Enckytraeus albidus, and others. Those canals 

 thus situated remind one of the trembling organs 

 of Rotatoria, connecting the two lateral canals 

 with the cavity of the body ; see above, § 138. 



6 With Lumbricus terrestris, and its allied 

 species, I have as yet been unable to find any ori- 

 fices of the aquiferous canals. Henle also {Mul- 

 ler's Arch. 1835, p. 5S0) has always found them 

 looped upon themselves. They may however exist, 

 although they have eluded the notice of Henle and 

 myself, for the respiratory organs of Lumbricus 

 are so difficult to study that there is yet no de- 

 scription or figure giving any idea of their com- 

 plexity ; see the poor figures of Lumbricus ter- 

 restris by Leo (luc. cit. p. 25, Tab. I. fig. 4), and 

 Morren (loc. cit. p. 53, U8, Tab. XIV. XV.). 

 Those of Hoffmeister, although more detailed, are 

 scarcely less unsatisfactory (loc. cit. p. 15, Tab. I. 

 fig. 35, 36). It now remains to inquire as to the 

 relations existing between these aquiferous canals 

 and the glands at their base which have been 

 taken by many for mucous pouches. I cannot, for 

 ray own part, perceive that these glands with the 

 Lumbricus terrestris, excrete any liquid what- 

 ever upon the ventral surfaoe. On the other hand, 

 I have often seen escape from the back of this 

 animal, a watery liquid which was only the con- 

 tents of the cavity of the bixly, issuing through 

 small orifices upon each side of the median line 

 between the segments of the body. Although I do 

 not know, yet I suppose, that similar orifices exist 

 with the other Lumbricini, and thus, by these ori- 

 fices and by those of the internal branchiae, the 

 necessary renewal of water for these last, can take 

 pla<Se. This hypothesis appears admissible since 

 the cilia of the aquiferous canals always move in 

 the aame way. 



*l§ 159, note 7.] See, for many details on 

 these parts, Gegenbaur (Ueber d. aogenaonten 



15* 



7 These vesicular dilatations do not pulsate, and 

 are undoubtedly analogues of the simple sinuses 

 which communicate with the aquiferous canals of 

 Nephelis vulgaris.* 



1 These respiratory organs may be taken as 

 analogous to the aquiferous vessels of the Lunibri- 

 cini, which can be everted so that the internal cil- 

 iated surface becomes external, and the e.xternal 

 blood-vessels internal. 



^' Serpula, and Protula. 



3 Sabella. 



4 Terebella ; see Delle Chiaje, Mem. loc. cit 

 Tav. XLIII. fig. 1-5, Tav. XLV. fig. 2, 10 ; and 

 Milne Edwards, Ann. d. Sc. Nat. X. 1838, p. 200, 

 PI. X. XI. fig. 1. There are here on each side of 

 the neck three multiramuse, contractile branchiae 

 which are placed close together. Into these a 

 large portion of the blood of the median dorsal ves- 

 sel enters by six lateral branches, while the re- 

 maining portion passes on through the dorsal ves- 

 sel to the tentacles and the borders of the lips. 



In each branchial tuft there are a simple artery 

 and a vein placed side by side, which anastomose 

 at its extremity in an arcuate manner. 



The returning blood from the six branchiae 

 passes by as many veins into the median dorsal 

 vessel, and the fre<iuent strong contractions and 

 dilatations of the branchiae, certainly very much 

 aid the current. 



5 Amphitrite ; see Pallas, Miscell. zool. p. 120, 

 Tab. I.X. fig. 1, 5, 6, 8, e, e ; Rathki, Danzig. 

 Schrift. loc. cit. p. 59, Taf. V. fig. 1, 3. Here the 

 four semi-pinnate branchiae are upon both sides of 

 the second and third rings of the body, and each 

 lamella contains a tightly-closed vascular net- 

 work. 



<> The filaments of these branchiae are very short 



Respirationsorgane d. Regenwurma, In SieboU 

 and Kalliker's Zeitsch. IV. p. 221). —Bd. 



