102 THE CATFISH. 



1) Just above the pharynx are two pads of teeth, the upper pharyn- 

 geals, one on each side of the median line. Below are the lower 

 pharyngeals, so situated as to meet the upper when the mouth 

 is closed. Feel of these pads. 



m) At each side of the head is a flap the operculum covering the 

 gills. It is supported by several opercular bones. Lift the flap 

 and examine the bony gill arches bearing the red gill filaments. 

 How many such arches are there ? On the borders of the gill 

 arches note the rows of hard, tooth-like projections constituting the 

 gill rakers. Do they occur on both margins of all the arches ? 

 Are the projections all of equal length ? Watch a live fish in a glass 

 jar until you understand the cause and the direction of the current 

 of water that passes over the gill filaments to aerate the blood. 

 What part would the gill rakers play in this respiratory process ? 

 The slits between the several arches are known as the gill 

 clefts. 



n) Just back of the barbels on the chin is a V-shaped fold of skin with 

 the open part of the V directed backward. This is the branchios- 

 tegal membrane. It is supported by a number of bony bran- 

 chiostegal rays. Determine the number and shape of these 

 rays. The narrow region at the apex of the V is called the 

 isthmus. 



o) Look for the anal opening a short distance in front of the anal fin. 

 Just back of the anus is the urino-genital aperture of the male, 

 a common exterior opening for the renal excretions and the repro- 

 ductive elements. In the female of the catfish the urinary duct 

 and egg duct open externally on separate papillae. We have 

 thus a means of distinguishing the sexes without dissection, 

 remembering that there are three separate openings in the case of 

 the female and only two in the case of the male. Is this true of all 

 common fishes ? 



MEASUREMENTS. With ruler and dividers take the following 

 measurements: Head, the distance from the tip of the snout to the 

 posterior angle of the operculum; snout, distance from tip of nose to 



