Gic/i? 



x ' 



_ 

 PREFACE. 



For the introductory study of the structure and physiol- 

 ogy of a typical vertebrate, there is no form better adapted 

 than the common frog. To be sure, the frog is not so gen- 

 eralized in structure as the more primitive urodele ; but this 

 slight disadvantage is offset by the greater ease with which 

 frogs may be obtained in large numbers, and the better de- 

 velopment of the hind limbs is favorable for the study of 

 muscles. Since the more specialized structures of the frog 

 are mainly concerned with its mode of locomotion, these 

 adaptations do not markedly affect the internal organs other 

 than the skeleton and the muscles. In order that the stu- 

 dent may realize in what respects the frog is modified from 

 the primitive tetrapod type, comparison of the form and 

 orientation of the body should be made with the more typi- 

 cal caudata; for this purpose articulated skeletons, as well 

 as entire specimens, should be used. 



The order of topics in this guide should be closely fol- 

 lowed, since it is planned to give a distinct picture of each 

 organ-system in its relation to the whole, with the greatest 

 economy of time and material. If the student has not had 

 previous training in biology, an exception should be made 

 in the case of certain histological topics; it is best to begin 

 the microscopical work with the study of some simple 

 tissues, such as epithelium, blood, cartilage and perhaps also 

 connective tissue and unstriated muscle fiber, before at- 

 tempting the study of cross-sections of such complex organs 

 as the intestine, stomach and kidney. An introductory ex- 



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