6 Invertebrate*. 



motion (though this has exceptions), in being only 

 capable of assimilating organic matter (except in the 

 case of water and oxygen), and in having their cell- 

 walls composed of nitrogenous matter, while in plants 

 non-nitrogenous matter abounds. Higher animals are 

 strongly differentiated from plants ; the lower forms are 

 often of doubtful position. Animals may be simple or 

 complex, complexity depending on division of labour, 

 and the consequent specialisation of function in organs 

 which become differentiated from each other. The 

 chief functions are Relation, Nutrition and Repro- 

 duction, the last taking place during the stage when 

 individual growth has ceased and while as yet repair 

 exceeds waste. 



CHAPTER II. 



ORGANS AND CLASSIFICATION OF ANIMALS. 



Method of Study. The first branch of zoology ne- 

 cessary to be studied is the anatomy of the organism, 

 and the best method of study is the examination of 

 some of the commoner types of each class. As many 

 of these are small, and optical assistance necessary, 

 the student should provide himself with a good pocket 

 lens. For dissection, the instruments required are, a 

 scalpel, a fine-pointed pair of dissecting forceps, and 

 several sharp-pointed needles fixed in wooden handles 

 and with their extremities ground to sharp edges so as 

 to cut as well as tear. As many small animals can be 

 most easily dissected under fluid it is convenient to 

 have a shallow wooden tray lined with gutta percha or 

 sheet lead for the purpose, while it often facilitates 



