THE TRANSITION TO LAND 



379 



are two reasons for this. First, the male has no copulatory organ to be 

 used for the transference of sperms into the body of the female, as do 

 most land vertebrates. Second, the amphibians have an egg which can- 



B 



Animal Biology, Wolcott, McGraw-Hill Book Company, Inc. 



Fig. 26.1. Salamanders. A. The mud puppy, Necturus. B. The larva of the tiger 

 salamander, Ambystoma. C. The adult of the tiger salamander, Ambystoma. 



not survive away from the water. To live and grow on the land, an egg 

 must have a thick, protective shell, and the embryo must develop special 

 membranes inside the shell to take care of respiration. Since the am- 

 phibian egg has neither, it must develop in the water. Amphibian eggs 



