io ECONOMIC ZOOLOGY AND ENTOMOLOGY 



tive tissue in which are series of small tubules that take out 

 much of the waste material from the blood that flows through 

 the kidneys. This waste material, urea, passes from the kid- 

 neys through the ureters into the cloaca and collects in the 

 sac-like bladder, from which it is finally expelled through the 

 anus. The skin, liver and the walls of the intestines take some 

 part in excretion, but the kidneys are the principal excretory 

 organs. By the side of the kidneys are the yellowish adrenal 

 bodies. 



In the region of the kidneys may be seen the reproductive 

 organs. In the female the ovaries, when filled with the small 

 black and white eggs, are very conspicuous. As these eggs 

 develop they break out into the body-cavity and find their way 

 into the open ends of the long convoluted oviducts. While 

 passing through the oviduct the eggs receive a coating of an 

 albuminous fluid which swells up when it reaches the water. 

 The eggs are collected in the posterior portion of the oviducts 

 and finally pass into the cloaca and out of the body. The 

 white ovoid testes of the male are attached to the ventral side 

 of the kidneys by folds of the peritoneum, which is a membrane 

 lining the abdominal wall. From each testis a number of 

 delicate tubes, called vasa deferentia, enter the kidney and be- 

 come connected with the urinary tubules. The spermatozoa 

 that are developed in the testes thus pass through the kidneys 

 and the ureters into the cloaca. The eggs are fertilized by the 

 spermatozoa which is poured over them while the female is 

 laying them. 



The Skeleton. The bones making up the skeleton of the 

 frog may be considered in two groups: the axial skeleton made 

 up of the skull and the vertebral column, and the appendicular 

 skeleton consisting of the bones of the fore and hind limbs and 

 the pectoral and pelvic girdles. The skull consists of the bones 

 forming the immovable upper jaw, the movable lower jaw, the 

 hyoid apparatus supporting the tongue, and a number of bones 

 joined together to form the narrow brain case. The vertebral 

 column is made up of nine vertebra followed by a slender bony 

 rod, the urostyle. Each vertebra consists of lateral transverse 

 processes and a firm central portion which surrounds the neural 



