ANNELIDA. 



171 



Fig. 73. 



especial manner subservient to respiration, are 

 simply a kind of papillae or laminated cutane- 

 ous productions very little or not at all sub- 

 divided, attached either to the extremity or 

 base of the feet and distributed in an almost 

 uniform manner over the entire length of the 

 body, (Jig. 64, /",,/,./) In the eunice, and other 

 allied genera, their position is the same, but 

 they assume the form of an elongated filament, 

 furnished with a series of prolongations of a 

 similar filiform shape, disposed like the teeth 

 of a comb, and traversed longitudinally by a 

 canal filled with red blood, (fig. 73, f.) In 

 the amphinomian family, 

 as in the former groups, 

 these branchiae are placed 

 on almost every segment 

 of the body, so that these 

 organs form along the whole 

 extent of the back a double 

 row ; but here their struc- 

 ture is more complicated, for 

 the filaments are extremely 

 subdivided, (fig. 63, /.) 

 In the arenicolts, the form 

 of the branchiae is almost 

 the same as in the amphinomes, but they are 

 limited in their position to the middle seg- 

 ments of the body. In the genus terebella 

 the branchiae are also highly ramified vascular 

 appendages to the integument, but their num- 

 ber is inconsiderable, and they are all inserted 

 near the cephalic extremity of the back. In 

 the serpulae, the membrane which forms a 

 sort of thoracic disc near the cephalic ex- 

 tremity of the body, ought to be regarded as 

 an organ of respiration, and it is probable that 

 the tentacles surrounding the mouth like a 

 crown of plumes are subservient to the same 

 function.* In the hirudinee respiration is in 

 part effected by the external skin, but there 

 exists in these annelida a series of small mem- 

 branous sacs, which communicate externally 

 each by a minute orifice situated on the ven- 

 tral aspect of the body : these sacs derive from 

 the numerous vessels which ramify upon their 

 parietes a considerable quantity of blood. 

 Water penetrates into these organs and seems 

 to subserve a true respiratory purpose. These 

 sacs are commonly denominated ' pulmonary 

 sacs,' and some authors think that they receive 

 into their interior atmospheric air in a gaseous 

 form. Their number varies from fifteen to 

 twenty, and it may be observed, when a living 

 leech is irritated after being recently removed 

 from water, that a small quantity of liquid 

 escapes from their apertures. 



In the lumbrici terrestres there is in like 

 manner found in each segment and on eitherside 

 of the digestive tube, an enteroid vessel folded 

 upon itself, containing a liquid and opening 

 outwardly by a particular pore. These sacs 

 are less vascular than in the leeches ; never- 

 theless there is reason to believe that they fulfil 

 an analogous office, and perform a more or less 



* See, for additional details, the works already 

 cited of Savigny, De Blainville, and Audouin and 

 Milne Edwards. 



important part in respiration. Lastly, it has 

 been proved that in the annelida there are 

 other pores, placed on the back, which tra- 

 verse directly the dermo-muscular envelope, 

 and communicate with a cavity intermediate to 

 the muscles and intestines, and imperfectly 

 divided by transverse septa, into which air or 

 water can penetrate. This structure may, 

 indeed, belong to the respiratory apparatus, 

 but science does not yet possess sufficient data 

 to solve that question. An analogous dis- 

 position has been observed in the na'is.* 



Generation. The generative apparatus is 

 only very imperfectly understood in the anne- 

 lida. It appears that all these animals are 

 hermaphrodite, but that they cannot fecundate 

 themselves ; the intercourse of two individuals 

 being necessary for the accomplishment of the 

 act of generation. It is in the earthworm and 

 leech that this part of their anatomy and phy- 

 siology has been most completely studied. 



In the leeches the sexual apertures are placed 

 at the inferior surface of the body towards the 

 anterior third, and separated from one another 

 by the intervention of five segments. The 

 anterior aperture belongs to the male organs, 

 and at the season of reproduction a filiform 

 and highly contractile penis is observed to be 

 protruded from that part, (fig. 74, 75, a.) 



F'g. 74. 



Fig. 75. 



n- 



side 

 there 

 body 



con- 



This communicates 

 ternally with a narrow 

 cylindrical canal (6), 

 which in its turn opens 

 into a kind of whitish 

 vesicle of a pyriform 

 shape (c) commonly cal- 

 led the vesicula semi- 

 nalis. On each 

 of this vesicle 

 is an oval whitish 

 (d) composed of 

 torted tubes filled with a whitish liquid : each 

 of these organs is a testicle; and they seve- 

 rally give origin to a slender vas deferens 

 (fig. 75, e~) of the same colour, which opens 

 into the vesicula seminalis. Lastly, from the 

 posterior extremity of the testicle, another fili- 

 form duct (/') is continued, which passes back- 

 wards on each side of the nervous cord, and 

 gives origin to a series of pedunculated vesicles 

 filled with a whitish fluid similar to that which 



* For the structure of the pulmonary sacs, see 

 Willis, op. cit. Thomas, ' Memoires pour servir 

 a 1'Histoire Nature-lie des Sangsues.' Home ' Lec- 

 tures on Comp. Anatomy,' Moquin Tandon, op. cit. 

 Morren de Lumbric. tcrrcst. Duges, op. cit. 



