480 



COLLEGE ZOOLOGY 



•v 



attached to the dorsal body-wall. The two testes of the male 

 are small ovoid organs suspended by membranes and lying at 

 the sides of the alimentary canal. The ovaries and oviducts of 

 the female occupy a large part of the body-cavity during the 

 breeding season. The coelom is lined with a mesodermal mem- 

 brane, the peritoneum (Fig. 409). The reproductive organs 



and alimentary canal are suspended by 

 double layers of peritoneum called mesen- 

 teries (Fig. 409, 1, 2, 3). 



The Digestive System. — The food of 

 the frog consists principally of living worms 

 and insects. These are usually captured 

 by the extensile tongue, which can be thrown 

 forward as shown in Figure 410. The object 

 adheres to the tongue, which is covered with 

 a sticky secretion, and is then drawn into 

 the mouth. No attention is paid to objects 

 that are not moving. Large insects are 

 pushed into the mouth with the forefeet. 

 If the object swallowed is undesirable, it 

 can be ejected through the mouth. 



The mouth cavity is large (Fig. 411). The 

 tongue (T) lies on the floor of the cavity 

 with its anterior end attached to the jaw 

 and its forked posterior end lying free. 

 When a lymph space beneath the tongue is filled, the tongue 

 is thrown forward for capturing insects (Fig. 410). The teeth 

 are conical in shape and are borne by the upper jaw and by 

 two bones of the roof of the mouth called vomers (Fig. 411, V). 

 They are used only for holding food and not for masticating it. 

 New teeth replace those that become worn out. 



The oesophagus opens into the mouth cavity by a horizontal, 

 slit (Fig. 411, 0); it is a short distensible tube leading directly 

 to the stomach. The stomach is crescent-shaped and lies mostly 

 on the left side of the body; it is large at the anterior or cardiac 



Fig. 410. — Three 

 stages of the movement 

 of the tongue of a frog, 

 Rana esculenta. (From 

 the Cambridge Natural 

 History.) 



