656 SUPPLEMENT ON 



especially the leeches ; while the absolute want of teeth in 

 the last division, ammoccetes, is analogous to the case of the 

 earth-worms, the arenicolae, serpulae, and terebella. There is 

 also a considerable analogy between the conical muscular 

 mouth, furnished with calcareous pieces, often serrated, 

 moving transversely in nereides, aphrodites, and the lampreys. 

 And the two transverse pectinated trenchant ranges of the 

 mouth of amphitrites assimilate that organ in these animals 

 to the mouth of the myxine. 



The circulating system of the suctorii is like that of fish, 

 with this difference, indeed, that all their vessels are attached 

 to the parenchyma of the different organs, into whose sub- 

 stance they proceed in the way these vessels do in the dura 

 mater, the bones and the liver of the true vertebrata. A 

 similar disposition of these vessels occurs in the leeches and 

 earth-worms. 



The respiratory organs in the lampreys and ammoccetes are 

 altogether different from that of most other fish, except the 

 sharks and rays. These organs are like those of animals 

 whose lungs are expanded laterally. In these, the cartilagi- 

 nous parietes of the thorax act as springs, tending constantly 

 outward, and consequently giving more space to the cavity of 

 the thorax, while at the same time their flexibility permits a 

 certain contraction. The power which the present animals 

 possess moreover of taking in and expelling the water by 

 the exterior orifices of the gills, presents a peculiarity dif- 

 fering altogether from what takes place in the respiration of 

 fish in general ; but in the annelida, we find a similar phe- 

 nomenon. 



The organs of generation in the annelida are very like 

 those of these fish. In the earth-worm, for example, the 

 eggs fall into the cavity of the belly, without the intervention 

 of any oviduct ; and they escape from the cloaca by small 

 openings for the purpose, as in the arenicolae and aphroditae 



