118 



THE COCKROACH 



stomach) is a rounded cushion set closely with hairs, and 

 between and beyond these are hairy ridges. (See fig. 61.) The 

 whole forms an elaborate machine for squeezing and straining 

 the food, and recalls the gastric mill and pyloric strainer of the 



Fig. 60. The Six Primary Folds (teeth) of the Gizzard, seen in profile. 



;'&-'' ,'fi' IV 



l&w' /f -^Sf- ' 



Fig. 61. Part of Gi?zard laid open, showing two teeth (T) and the intermediate 

 folds, as well as the hairy pads below. A A and B B are lines of section 

 (see figs. 62 and 63). X 50. 



Crayfish. The powerful annular muscles approximate the teeth 

 and folds, closing the passage, while small longitudinal muscles, 

 which can be traced from the chitinous teeth to the cushions, 

 appear to retract these last, and open a passage for the food.* 



* Plateau has expressed a strong opinion that neither in the stomach of Crustacea 

 nor in the gizzard of Insects have the so-called teeth any masticatoiy character. 

 He compares them to the psalterium of a Ruminant, and considers them strainers 

 and not dividers of the food. His views, as stated by himself, will be fouud 

 on p. 131. 



