PROBLEM 2. Honj) More Complex Ainmcils Reproduce 



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Fig. 378 Baby S7iapping turtles. Reptiles have internal fertilization. In some kinds, 

 the eggs hatch inside the female's body, but most reptiles lay eggs that are covered 

 with a leathery shell. (American museum of natural history) 



you would find the little front legs al- 

 ready formed under the skin. Its organs 

 of digestion and circulation are different 

 from those of the parent frog; they too 

 undergo changes. Within the two- 

 chambered heart a wall grows, making 

 three chambers. The long, coiled diges- 

 tive tube gradually forms a true stomach 

 and intestine, much shorter than the 

 original tube. Lungs form; the gills dis- 

 appear. The tail gradually grows shorter. 

 It is absorbed or in other words it is used 

 as food while the tadpole is changing. 

 Tiny teeth appear in the mouth and the 

 long tongue develops. The animal now 

 feeds on insects and spends part of its 

 life on land. When it is swimming and 

 floating in the water, it must come to the 

 surface from time to time to breathe, 

 even though it gets some oxygen 

 through its skin. In its habits and its ap- 



pearance it is very different from the 

 tiny tadpole that hatched from the t^g. 

 When striking changes of this sort occur 

 between the embryo stage and the adult, 

 the development is called a metamor- 

 phosis. 



Reproduction in land-living animals. 

 In animals that live their whole lives on 

 land, or in amphibious animals that re- 

 produce on land, fertilization takes place 

 inside the body of the female. If this 

 were not the case, these species would 

 have died out since eggs and sperms dry 

 up and die when exposed to air. In inter- 

 nal fertilization the male puts the sperms 

 directly into or near the oviduct of the 

 female. The sperms are in a liquid me- 

 dium when they are introduced. By lash- 

 ing their tails they can swim to the t<^<g 

 cells which have passed from the ovary 

 into the oviduct. There may be one or 



