172 



THE ANNELTDES. 



§159. 



§ 159. 



With the Hirudinei, and Lumbricini, the peculiar canals found in the 

 abdominal cavity may be regarded as internal branchiae, or as aquiferous 

 vessels. 



The intimate structure of this aquiferous system is difficult to unravel 

 with the Hirudinei. It is most easily observed with the Branchiobdella ; here 

 there are only two pairs of curved canals whose inner surface is ciliated. 

 One of these pairs opens upon the ventral surface at the beginning of the sec- 

 ond third of the body, while the other opens at the extremity near the median 

 line. Each of these four canals is dilated just before its external opening 

 into a round, yellow cavity, from which pass off many loop-like vessels. '^^ 

 With the other Hirudinei, these organs in pairs are more numerous, and 

 situated one after another from the second third to the extremity of the 

 body. 



It is remarkable that the ciliated epithelium lining these canals with Bran- 

 chiobdella, is absent in all the other species.*-' 



The structure of the respiratory system of the Lumbricini is not less 

 difficult to be understood. With all the genera there are, at the commence- 

 ment and on each side of the intestine, very tortuous canals which open 

 upon the ventral surface, by a narrow orifice near the median line. These 

 canals are lined with long cilia which have an undulatory movement ; *^' 

 they also are colorless and sometimes have dilatations before opening exter- 

 nally, but they never contain air, so that the terms tracheae or pulmonary 

 cells, have been erroneously applied. <■*' Often they float loosely in the 

 cavity of the body, and their free extremity has an orifice surrounded by 

 long vibratory cilia.''' With some", however, they terminate by thickly- 



1 See Henle, in MuUer^s Arch. 1835, p. 576, 

 Taf. XIV. fig. 1. This epithehum would undoubt- 

 edly favor the constant renewal of water in these 

 canals. 



2 With Sans^uisuga, there are seventeen pairs 

 of these organs. They have been taken by Brandt 

 (Med. Zool. II. p. 251, Taf. XXIX. A. tig. 55-58) 

 for organs of special secretion, since he has seen a 

 whitish liquid escape from their ventral orifices. 

 The riband-like organ of these Annelides is not, 

 moreover, as is usually supposed, a simple canal, 

 but is composed of numerous interwoven and fre- 

 quently interanastomosing canals, having no trace 

 of ciliated epithelium. 



From Diigis^ remark (Ann. d. Sc. Nat. XV. 

 1828, p. 303, PI. VIII. fig. 2), I think it probable 

 that this net-work is formed of blood-vessels whicli 

 are occasionally empty, for I have always found 

 them colorless. 



In this case, the real aquiferous canals are prob- 

 ably concealed in the net^work, and from then' want 

 of ciliati-d ciiitli-lium not easily seen. 



With Nrphclis vulgaris, I have seen the same 

 number of internal branchiae as with Sanguisaga. 

 Here, the aquiferous system appears as a knot of 



colorless, non-ciliated canals connecting with a 

 vesicular pouch which is filled with red blood ; so 

 that in the posterior two-thirds of the body there 

 is a double row of seventeen sanguineous sinuses, 

 inside the lateral vessels. These siimses, already 

 carefully described by Mailer {MeckeVs Arch. 

 1828, Taf. I. fig. 1), take no part in the pulsations 

 of the main vessels, and are not alternately emp- 

 tied and filled during the transverse cii-culation of 

 these animals. 



A very interesting fact to me, is the existence 

 with this Nephelis, of a multi-lobulate, resetted, 

 ciliated, colorless organ in the interior of these 

 sanguineous sinuses.* 



3 See Henle, in Mailer's Arch. 1837, p. 84, Taf. 

 VI. fig. 7, 8, V. w (Enchytraeus) ; and Gruithui- 

 sen, Nov. Act. Acad. Nat. Cm-. XI. 1823, p. 238, 

 Tab. XXXV. fig. 1, i., XIV. 1828, Tab. XXV. fig. 

 5 (TVals and Chaetogaster). 



■i An aqueous respiratory fluid circulates iu 

 these canals undoubtedly by the aid of cilia. The 

 terrestrial Lumbricini which live only in the damp 

 earth obtain this fluid therefrom. 



5 I have observed this with Saemiris varie- 

 gata, Lumbriculas variegatus, Nats elingui.i. 



* [§ 153, note 2.] See, upon the circulatory sys- 

 tem of BrancAe//i'o?i, Quairey'ag'es (Ann. d. Sc. 

 Nat. XVIII. 1852, p. 314). According to him, the 

 general cavity of the b'ldy here, is represented by 

 a collection of canals which are lacunae. This 

 forms a vascular lymphatic system which circulates 

 chyle to the branchiae ; these last are, therefore, 

 " hranchies lymphatiques." 



He also states as conclusions : 



1. The non-communication of the abdominal ves- 

 sels with the branchiae. 



2. The existence of a subcutaneous lymphatic 

 vessel. 



3. The origin from this vessel of trunks which 

 go to the branchiae. — Ed. 



