io6 A GUIDE FOR THE STUDY OF ANIMALS 



The mouth may be kept open by a short splinter or a 

 ball of paper. 



The pupil should identify the following structures : — 



1. Gill, an organ for breathing the air dissolved in 

 water. 



2. Gill arch, an arch of bone or cartilage supporting the 

 gills. 



3. Gill filaments, fringe-like structures attached to the 

 gill arches, forming the gills. 



4. Gill raker, lateral projections from the gill arches. 



5. Gill-slits, openings between the gill arches for the 

 passage of water. 



6. Operculum, the flap-like covering of the gills on 

 each side of the head. 



Questions. 



1. Compared with the size of its body, how wide can 

 the fish open its mouth } What do you infer as to the 

 size of its " bite " .' 



2. Are the jaws rigidly affixed to the skull.' Why 

 should they be so attached, or why not .' 



3. Of how many pieces is the upper jaw composed .' the 

 under jaw .' 



4. Where are the teeth } Judging from their form, 

 size, and situation, what do you think must be their use .'' 



5. Do you think the tongue is used to assist in masti- 

 cation .' in tasting .' in speech .' in swallowing } 



6. How many gills are there, and where are they 

 situated ? How are they attached ? Which one is not free 

 from the body throughout its length ? 



7. What probably causes the color of the gill filaments .'' 

 What is there in their number and texture which fits them 

 for their function ? 



