ANNELIDA A]ST> CRUSTACEA. 1/3 



female genital parts at r, the male organs at s, and the anal 

 sucker at o. 



[ 324. In some annelida the mouth is provided with a pro- 

 jectile proboscis, formed of the anterior part of the intestinal 

 canal (fig. 233). This organ can be protruded and inverted 

 like the finger of a glove, and, like the proboscis of predacious 

 mollusca, has a set of muscles consecrated to effect its move- 

 ments ; in the Nereis it is very complicated, its free extremity 

 being armed with long jaws, like the pincers of Crustacea. 

 The proboscis is regarded by some physiologists as a pharynx, 

 armed with teeth, like those of star-fishes and echini ; and 

 being like them, capable of eversion. The stomach of Nereis 

 is large, and from its posterior part two csecal appendages pro- 

 ject ; its inner surface is armed with two small white teeth ; 

 the intestine passes straight through the body, and terminates 

 in an aperture at the posterior part. 



In the Arenicola, or sand-worm (fig. 233), we observe an 

 additional complication of structure ; to the short esophagus 

 succeeds a complicated stomach, the first portion of which is 

 simple, and the second very complex ; into the latter division 

 of the organ an immense number of branched appendages 

 open, which appear to be a repetition of the biliary caeca ob- 

 served in the star-fish ; the stomach passes imperceptibly into 

 the intestine, which terminates at the posterior part of the 

 body. In the Aphrodita aculeata, or sea-mouse, a similar 

 arrangement of the internal organs exists. 



[ 325. In the CRUSTACEA the digestive organs, when com- 

 pared with those of the annelida, present a greater develop- 

 ment of the organs of mastication. The jaws, which are nume- 

 rous, move horizontally by powerful muscles ; the mouth of 

 the lobster and crab is situated on the under surface of the 

 body, on each side of which we find the first pair of jaws ex- 

 panded into a broad form, and sending out behind long pe- 

 dicles for the insertion of powerful muscles, which have 

 their points of attachment at the internal surface of the dorsal 

 shield ; succeeding these we find a second, third, fourth, fifth, 

 and sixth pair of jaws : they are all, especially the three first 

 pair, provided with sensitive palpi, in which it is probable 

 the sense of taste resides. The esophagus is short, opening 

 into a singularly complicated stomach, extended on a carti- 



