(b), Homocercal — Study and draw tail of 



the halibut, 

 (c). Isocercal — Study and draw tail of the 



cod. 

 (d). To which type does the tail of the 

 perch belong? 

 (3); Finlets — Small and flaglike fins of the dorsum 



and venter cephalad of the caudal 



fin. Examine a mackerel. Draw 



the tail region. 

 (4). Structure of fins. 



(a) . Types of fin-rays. 



(i). Soft rays. Ask the instructor 

 for a fin composed of soft 

 rays. Note the method of 

 branching and the joints. 

 Make a drawing of a single 

 ray. 



(2). Spines. Ask for specimen. 

 Cornpare with soft ray. 

 Result? Examine the first 

 dorsal fin of the miller's 

 thumb. To what type do 

 the rays belong? Examine 

 the brook stickleback and 

 note the spines on the dor- 

 sum unconnected by mem- 

 brane. These are termed 

 free spines. 



(3). Fulcra — Rudimentary spine- 

 like projections on the 

 cephalic margin of a fin. 

 Examine the dorsal of the 

 gar. Draw. 



(4). Examine the dorsal fins of the 

 common bullhead. Note 

 that the last dorsal fin is re- 

 duced in size and lacks rays. 

 Such a fin is known as an 

 adipose fin. Compare the 

 adipose fin of the bullhead 



