198 GENERAL ZOOLOGY 



the esophagus (Fig. 100, 10, 11). Before the ingested (swal- 

 lowed) food reaches the crop (Fig. 100, 12) the secretion, and 

 sometimes even hard particles from the calciferous glands 

 (Fig. 100, 15, 16), mixes with it and probably serves to neutral- 

 ize whatever acid may be present, and helps to maintain the 

 contents of the oesophagus in an alkaline condition, so that 

 the digestive fluid of the intestine (Fig. 100, 14), which is 

 alkaline in chemical nature, can act without interference. 

 The crop is a temporary reservoir for the food, and the gizzard 

 (Fig. 100, 13) is the only place in the entire digestive system 

 adapted for dividing large particles of food into minute pieces. 

 Earthworms are known to swallow small, rough pebbles, and 

 even sharp pieces of glass, for the purpose of using them in 

 the gizzard to grind into bits other particles which are swal- 

 lowed as food. The strong muscles in the wall of the gizzard, 

 by corseting, grind the contents together, and every particle 

 is worn smaller. 



The process c LigestiOn in the earthworm begins " r hmi. 

 s on seizing food with its lip, the animal pours out a secretion 

 from glands 'iii "tire ^hurvnx. Digestion continues .as the food 

 is being drawn into the pharynx, ana Wiiiie on "its \va_> f h rough 

 the oesophagus. Experiments with the digestive fluid of etrth- 

 worms indicate that it has a chemical action on the thivt 

 principal classes of organic foods, namely, proteids, carfa 

 hydrates, and /ate. The proteids which the earthworm T 

 be likely to devour are bits of muscle of very small animals, 

 and protoplasm, the living cell-substance of both animals and 

 plants. The carbohydrates, such as the starch-granules or 

 the sugar of any vegetable cell, form a large portion of its 

 food, while fats are eaten probably in small quantities. 



The digestive fluid of the earthworm resembles the digest- 

 ive fluid of the higher animals, not only in being capable of 

 acting on the three important classes of organic foods, but also 

 in containing some of the same special chemical compounds 



