134 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



oes. 



n.c. 



pharynx is passed onwards by what are termed peristaltic contractions 

 of the enteric wall, waves of constriction — produced by the contraction 



in succession of the circular 



b.C: * s,o.g. muscles — passing tailwards 



and pushing the contained 

 food in the same direction. 

 In the gizzard, where the 

 muscular coat is specially de- 

 velopedj the food undergoes a 

 process of grinding into pulp. 

 The food during its onward 

 progress is subjected to the 

 action of various secretions. 

 The actual process of diges- 

 tion is mainly carried out in 

 the intestine and the digestive 

 ferments are produced by 

 gland-cells which are scattered 

 about in the endoderm and 

 pour their secretions into the 

 intestinal cavity. In the region 

 of the oesophagus (about seg- 

 ments X-XII) special collec- 

 tions of gland-cells are found 

 in three pocket-like outpush- 

 ings of the enteric wall (Fig. 

 65, A, eg). These are the 

 calciferous glands, so called 

 from the nature of their secre- 

 tion — calcium carbonate — 

 which gives the glands a very 

 characteristic white chalky 

 appearance. The function of 

 this secretion is apparently to 

 neutralize the free acid so 

 frequently present in the soil 

 which the worm ingests. 



Between the enteric wall 

 and the body-wall is the wide body-cavity or coelome (Fig. 63, 

 coeJ), divided into numerous compartments — one to each somite — 

 separated by thin transverse membranous partitions or septa, and 



an. 



B 



Fig. 65. 



Dissections of Lumbricus, seen from the dorsal side. 

 A, to show alimentary canal ; B, to show central 

 nervous system, an, Anus ; b.c, buccal cavity ; c, crop ; 

 c.g^ calciferous glands ; g, gizzard ; int, intestine ; n.c, 

 nerve-cord ; oes, oesophagus ; ph, pharynx ; s.o.g , 

 supra-oesophageal ganglia. 



