20 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



F. FUNCTION OF THE CIRCULATORY SYSTEM; CIRCULATION OF THE BLOOD 



The food prepared in the digestive tract and the oxygen taken in through 

 the lungs must be carried to all parts of the body; and the waste materials from 

 these parts conveyed to the kidneys and lungs. Such transport of materials is 

 the function of the circulatory system. 



Demonstration of the circulation of the blood. In the web of the frog's 

 hind foot, spread out under the microscope, observe the following: 



1. The network of tubes, the blood vessels, in which the blood flows. 



2. The composition of the blood. It consists of solid bodies, the corpuscles, 

 which may be seen shooting along the vessels, and the colorless fluid, the plasma, 

 in which they are suspended. 



3. The arteries, vessels in which the blood flows from the larger vessels into 

 their smaller branches. 



4. The veins, vessels in which the blood flows from the smaller into the 

 larger vessels. 



5. The capillaries, the smallest vessels, forming a network, in which the 

 direction of flow is indefinite. 



6. The pulse, rhythmic jerks in the blood stream, due to the heart beats, 

 observable only in the arteries. 



7. The chromatophores, the small black bodies in the skin. They may 

 exhibit various shapes. In the contracted state, they are round black masses; 

 in the expanded state, they show long, delicate, spidery processes. 



G. FUNCTION OF THE REPRODUCTIVE SYSTEM; REPRODUCTION, 

 DEVELOPMENT, THE LIFE-CYCLE 



The ovaries produce the female elements, which are called eggs or ova, and 

 the testes produce the male elements, which are called spermatozoa. Before the 

 egg can develop it must unite with a single spermatozoon, a process known as 

 fertilization. The fertilized egg then undergoes a process of development which 

 results in the production of an individual like the one from which the egg arose. 

 The complete history from one individual to the next is called ontogeny, or the 

 life-cycle. As the life-cycle of the frog occupies too great a period of time for 

 its completion, the life-cycle of an insect will be studied instead. For this pur- 

 pose either the small fruit fly (Drosophila) or the common blowfly may be used. 

 The latter is preferable owing to its larger size but is available only during the 

 warm months. If Drosophila is to be used, each table will be given a bottle 

 containing a pair of fruit flies and a piece of banana as food. If blowflies are 

 to be used, a bottle will be provided containing two or three inches of moist sand; 

 put a piece of liver in it and set it near an open window. Watch the gathering 

 of flies about the bottle and observe, if you have time, the laying of eggs upon the 

 liver by the female flies. Then stopper the bottle with a wad of cotton. 



