590 BIOLOGY. 



The gills are not unfrequently covered with pergamen- 

 taceous scales, as in many Nereides, and especially in 

 Aphrodite. 



Fam. 6. Actinioid Worms AuchenobrancJdata. 



Body inclosed within a pergamentaceous or calcareous 

 tube with lateral bristles, branchiae and tentacula upon 

 the neck or head. 



The neck is surrounded by a kind of mantle, almost 

 as in the Snails, so that several animals have been 

 arranged here, which are now known to be veritable 

 Snails. Upon the head many have a horny operculum, 

 whereby they can close the shell. 



Here belong the Amphitritse, Terebellse, Serpulae, and 

 Sabellse. 



Order 3. Acaleplian Worms Sternwiirmer. 



3506. These creatures attain the most perfect struc- 

 ture of the Worms. The blood is white, the form cylin- 

 drical, globular and stellate ; the mouth surrounded by a 

 ring or wreath of maxillae. The nerves form a ring 

 around the pharynx, and upon the latter are placed 

 membranous cysts, which spirt water into the tentacula 

 or feet as they have been called, and thereby expand 

 them. 



It is impossible for these animals to continue to range 

 with the Acalephse, although they resemble them in 

 outward form ; for they consist of two cysts, the intestine 

 having become freed from the outer one as a special sac ; 

 moreover, they have a perfect vascular system, distinct 

 muscles, a mouth with a dental apparatus, which pre- 

 figurates a complete skeleton, a peculiar vascular system 

 for the injection of the tentacula or feet, a nervous ring 

 surrounding the pharynx, an ovarium entirely separated, 

 and lastly, a perfectly annulate body. 



Fam 1 . Pliysalial Worms, Holotliurice . 



Body cylindrical, very plentifully supplied with muscles. 

 Mouth and anus present, the former of these being sur- 

 rounded by a dental wreath and ramified branchimorphous 

 tentacula; branchiae upon the intestine, and branchial 



