THE VERTEBRATE BODY 



353 



and gather in large groups. The females are usually distinctly larger 

 and their bodies are distended with eggs at this season. The smaller 

 males have an enlargement on the inner digit of the front legs which 

 distinguishes them from the females. The males develop the clasping 

 instinct at this time and climb on the backs of females and clasp them 

 around the body with their front legs. This instinct is so strong that the 

 body of the male can be cut in two and he will still retain his grip. He 

 will retain his hold until the female lays her eggs which may be several 

 days later. When she feels the urge she dives in the water and, probably 



Bowman's 

 capsule 



Glomerulus 



Artery 



Tubule 



Fig. 24.4. Diagram of a renal collecting unit in the cortex of the kidney. Water and 

 dissolved minerals are squeezed out of the capillaries in the Bowman's capsule. Some 

 of the water and minerals needed by the body are then reabsorbed by the capillary bed 



at the loop of the tubule. 



aided by squeezing from the male, lays her eggs. As the eggs are laid 

 the male is stimulated to release his sperms which settle down and fer- 

 tilize the eggs. The male has no copulatory organ, so there can be no 

 internal fertilization and water is necessary for the sperms to swim to 

 the eggs. The further development of the eggs is discussed in Chapter 

 33. After releasing the sperms, the male loses his clasping instinct, in 

 fact loses his interest in the female altogether, and releases his grip and 

 goes his separate way until he feels the biological urge again the follow- 

 ing spring. 



Internally we find the reproductive systems given over to the pro- 

 duction of gametes and the release of them from the body. In the male 



