THE BASIS OF THE CLASSIFICATION OF TO-DAY 513 



termined from their structure, embryology, habits, habitat, ability to 

 crossbreed with related forms, and from certain other facts. 



By structure is meant the shape and arrangement of the parts of a 

 plant or animal. Certain plants are grouped together because they 

 have chlorophyll ; certain animals are classified together because 

 they have six legs. The embryology of a plant or animal refers to 

 its development from the time it is first formed until it is a full- 

 grown adult. A caterpillar looks somewhat like a worm which is 

 really one of the stages in the life history of an insect. Plants and 

 animals that have similar embryological developments are closely 

 related ; those with dissimilar embryological developments are 

 not closely related. Animals and plants which are closely related 

 usually have some similar habits. In general, most water plants 



N. Y. Zoological Society 



The duckbill (Ornithorhynchus anatinus) is an egg-laying mammal, native of Australia. It is 

 covered with dark fur, and has a bill and five-toed webbed feet. 



