ANIMAL ACTIVITIES. 
170 
fin along the median ventral line is the anal or ventral 
fin. The fin at the end of the tail is the caudal fin. 
Sketch a fish with fins extended. Indicate the names 
of the fins. 
Of what use are the bones in the fins (fin-rays)? 
Does the fish swim by using its fins, or its tail, or 
both ? 
The Head. What organs of sense do you find ? 
The ears are internal. 
Are the eyes movable ? Do they have lids ? How 
does the eye of the fish resemble the eye of man ? of 
the grasshopper ? How does it differ from these ? 
Do the nostrils open into the mouth ? Use a tooth¬ 
pick for a probe. Are the nostrils of use in breathing ? 
Of what use are they ? 
Does the mouth open vertically, or laterally ? Where 
are the teeth situated ? What is their shape ? What 
about the shape and position of the tongue ? 
Gills and Heart. What movements does the fish 
make while breathing ? 
Raise the gill-cover of the specimen on the bench. 
Tow many gills do you find ? How many gill-clefts 
:>r spaces between the gills ? 
The bony supports of the gills are called branchial 
arches. The soft delicate red branches from these 
arches are the gill-filaments. In these the blood is 
purified. What is the color of the blood of a fish ? 
Can you see the branchial arches by looking into the 
mouth of a fish ? 
Remove the skin and muscular walls from that por¬ 
tion of the ventral cavity directly behind the gills. 
T his exposes the heart. Can you see the swellings 
indicating the two cavities of the heart, the auricle and 
the ventricle ? The ventricle has the form of a tri¬ 
angular pyramid. The auricle is thin-walled and filled 
with venous blood, hence it looks like a clot of blood 
attached to the ventricle. The large blood-vessel 
from the heart to the gills is the ventral aorta. Its 
