48 COMPARATIVE ANATOMY. 



lips, with tactile appendages, as in Serpula. The canal is 

 placed in the axis of the body, having no convolutions, as in 

 Lumbricus (earth-worm), or possessing them, as in Sipunculus. 

 It may be comparatively a simple tube, as in Lumbricus, 

 though frequently sacculated, as in Hirudo, leech (q. v.). 

 Anus dorsal. Walls of canal are very muscular, a free peri- 

 staltic motion commonly present. 



Glandular appendages in the form of follicles surrounding 

 the commencement of the intestine, as in Sangitisuga, or a 

 defined gland emptying into the pharynx, as in Lumbricus, 

 a secretion analogous to saliva. A hepatic secretion, con- 

 stantly present, is elaborated from simple cells aggregated 

 upon the walls of the intestinal tube. 



Crustacea. Mouth with numerous appendages. (See 

 Teeth.) Stomach is a simple dilation, possessing a crushing 

 apparatus which is either simple, as in Limulus (king-crab), 

 or complicated and composed of three denticulated chitinous 

 pieces, which are moved upon one another by the muscular 

 coat of the stomach, to crush any intervening substances, as 

 in Homarus (lobster). Intestine extends along the axis of the 

 body without convolutions, and narrows as it terminates at 

 the anus. 



Salivary secretion rarely present, as in Lepas (barnacle). 

 Hepatic secretion is poured into the canal from simple fol- 

 licles at varying points, as in Daphnia. With the higher 

 forms a liver is observed, having a distinct duct, as in 

 Homarus. 



Myriapoda. Stomach rather long and intestine simple. 

 Salivary glands generally in two pairs on either side of the 

 oesophagus and stomach, opening into mouth. 



Arachnida. Intestine may be simple, extending without 

 any divarication to anus, as in Buthus (scorpion), or with 

 diverging caeca, as in Epeira. These may extend into the 

 feet (phlebenterism), as in Galeodes; the terminal portions of 

 the cseca communicating with the circulatory system, direct 

 transmission of chyle into the circulatory fluid is secured. 

 Termination of canal at end of oesophagus, allowing the fluid 

 food to pass from this point directly into the soft parts, of the 



