chap, iv.] DIGESTION IN EARTHWORMS. 



[cex 



portion of their intestine which is known as the 

 gizzard, are able to pound the food 

 which has been taken into it ; the 

 same phenomenon is known to be 

 observed in grain-eating birds. But 

 this is not the only method by means 

 of which the earthworm, with its un- 

 armed mouth, is able to act on the so 

 often dry food on which it lives ; as 

 Mr. Darwin pointed out, we observe 

 in them a case of extra-stomachal di- 

 gestion, which, so far as is known, is 

 unique in the animal kingdom. Before 

 proceeding to swallow its food, the 

 worm bathes it in a fluid secreted by 

 the glands of the mouth ; this has not 

 merely a lubricating, but a distinct 

 chemical action, the contents of the 

 cells and the starch granules being, in 

 some observed cases, dissolved out be- 

 fore the leaves were taken into the 

 mouth. The parts of the leaves thus 

 acted on seemed to be sucked into the 

 mouth by the action of the muscular 

 pharynx (Fig. 56) ; as the food passes 

 down the completely straight intestine, 

 it meets in the oesophagus with the 

 secretion of three pairs of calciferota s 

 glands, in which we find crystals or 

 concretions of carbonate of lime. It 

 would appear that these glands are 

 first of all excretory organs, but the 

 excretion seems to have a definite 

 action on the food, and to prepare it 

 for the action of the gastric juices. 



The secretion of the cells of the 

 intestine, by the action of which the 



Fig. 56. Diagram 

 of tbe Alimen- 

 tary Canal of an 

 Earthworm. 

 (After Ray Lan- 

 kester. ) 



m, Mouth ; pTi, pha- 

 rynx ; ces, oesopha- 

 gus ; eg, calcareous 

 glands ; cp, crop ; g, 

 gizzard \i, intestine. 



