BLOOD-VESSELS. 127 



5. The stomach-intestine (.9.?), corresponding to both the 

 stomach and intestine of higher animals. It is a straight, 

 thin-walled tube extending from the gizzard to the anus. As 

 food passes along this tube it is first digested in it, then absorbed 

 from it ; and finally the residue of refuse matters is voided at 

 the anus. We cannot distinguish any dividing-line, however, 

 between the region where the food is principally digested (stom- 

 ach) and the part where it is principally absorbed (intestine). 

 Probably both processes go on along its entire length, but diges- 

 tion, as might be expected, appears to be carried on especially in 

 the anterior part. 



The surfaces of the stomach-intestine are largely increased by 

 the presence of lateral pouches or diverticula, one on either side 

 in each somite. In front these are large and conspicuous, but 

 behind they gradually diminish in size until scarcely perceptible. 



The inner surface of the stomach-intestine is further increased by a 

 deep inward fold, called the typlilosole, running longitudinally along the 

 dorsal median line. The typhlosole is not visible on the exterior, but is 

 seen by opening the stomach-intestine from the side or below, or upon 

 making a cross-section. The outer surface of the stomach-intestine is 

 covered above, at the sides, and within the typhlosole, by yellowish-brown 

 cells, which are most abundant in the anterior portion. These cells are 

 believed to be of a glandular nature, their office being to separate from the 

 blood certain substances which are of use in digestion. They have been 

 compared to the liver of certain animals, but probably the comparison 

 is not very accurate. Hence the non-committal term ' ' cMoragogue cells" 

 has been proposed and is used for them. 



Circulatory System. The distribution of absorbed food-matters 

 is effected in the earthworm by two different devices. 



1. Codomic. The cavity of the coalom is filled w^ith a color- 

 less fluid which must be regarded as a kind of blood, and the 

 dissepiments are perforated by irregular openings, and the coe- 

 lomic fluid is probably driven back and forth through all parts 

 of the coelom. As the digested food is absorbed from the stomach- 

 intestine a considerable part of it is believed to pass into the 

 coelomic fluid, and is thus conveyed directly to the organs which 

 this fluid bathes. The coelomic fluid is composed of two con- 

 stituents, viz., a colorless fluid called the plasma, and colorless 

 isolated cells or corpuscles which float in the plasma, and are 

 remarkable for the fact that they undergo constant, though slow. 



