CHORDA TA. 



2 79 



ing questions will suggest the kind of studies that the student should 

 outline for himself: Do the appendages unite directly to the axial 

 skeleton? How many vertebrae are there? What is a single verte- 

 bra like? How much difference is there between those least alike? 

 Are there any ribs? How many bones in the hind leg? How do 

 the joints work? How much of the skull is brain-case? How does 

 the lower jaw work ? What makes the frog's head so broad? Where 

 are the teeth? How many parts in the sternum or breast-bone? 

 How much cartilage do you find about the skeleton of the frog? 



The study of the central nervous system will require a second 

 specimen. The most careful dissecting is necessary to cut away the 

 flesh and bone from the back of the skull and veitebrae in such a way 

 as to show the brain and spinal cord without injury. If this is 

 done, the following questions, among others, should be answered: 

 Is the nervous system bilaterally symmetrical? Why? Where is 

 the most of the nervous matter located ? Why ? How many regions 

 are there to that part of it that is in the skull ? Which is the largest 

 of these lobes? By lifting up the brain, beginning at the front, 

 examine the sides and bottom of the brain for nerves. How many 

 pairs do you discover? Do any nerves arise from the spinal cord? 

 Compare with those studied in the body cavity. 



After drawing all that you have found, compare your work with 

 figures and descriptions in the larger texts, and label your drawings. 



D. The Life History of the Frog. A most interesting series of 

 studies may be made by beginning in March or April to collect the 

 eggs from the ponds. Either watch them day by day in the ponds 

 or, better, arrange some large vessels in the laboratory, where the 

 eggs may be hatched. Some green water plants will be of advan- 

 tage in the vessel. Keep accomit of all the changes and the time 

 required for them. Study the activities, as breathing, feeding, sensi- 

 tiveness and the like in the tadpoles. The circulation of the blood 

 may be studied in the young tadpoles, in the gills and the tail. 

 Find specimens outside beginning to develop legs. What becomes 

 of the tail ? What becomes of the gills ? 



292. Classification. The principal divisions of the 

 Vertebrates are : 



Class i. Pisces (e. g., sharks, lung-fishes, bony fishes). 

 Page 281. 



Class 2. Amphibia (frogs, toads, newts, salamanders). 

 Page 296. 



