44 A MANUAL OF ZOOLOGY 



tection to the gills than the dog-fish has? Make a draw- 

 ing Illustrating the parts of the operculum. Raise the 

 operculum and examine the gills. There, is a double row 

 of gills on the posterior edge of each gill arch and a single 

 row of gill rakers on the anterior edge. How many gill 

 arches and gill-clefts are there? Depress the tongue with 

 the fingers and note the effect on the gills. What is the 

 meaning? On the inside of the operculum find a fleshy 

 projection, the false gill. Dorsal to the attachment of the 

 pectoral fin, note a sort of rudimentary operculum. 



I How many paired and unpaired fins has this fish? 

 Are the paired fins much developed? Notice the differ- 

 ence in the character and 'the placing of the pelvic fins 

 as compared with those of the dog-fish. Make the same 

 obseryations with regard to the other paired flns. From 

 these observations do you think that . this fish should be 

 placed higher or lower in the animal scale than the dog- 

 fish? Are there modifications of the fins by which the sex 

 may be known? In this regard which seems to be higher 

 or lower in the scale? Determine something of the man- 

 ner of the articulation of the paired fins by working them. 

 Can you detect the presence or absence of pectoral and 

 pelvic arches? Note the difference between the -dorsal 

 and the pectoral fin rays. The tail ,is hompcercal. What 

 does that mean? ; 



Are .the scales imbricated or are they tessellated? 

 Raise a scale carefully and note the thin epithelial mem- 

 brane reflected from its hinder portion to the scale under- 

 neath. Note- the pigment granules in this membrane. Re- 

 move a jpatch of scales and examine the flesh underneath 

 to determine the method of attachment. . Examine a num- 

 ber of scales under the hand lens. Make an enlarged 

 drawing of a typical scale, showing the shape and mark- 

 ings. Imbricated scales are either cycloid or ctenoid; 

 ctenoid if the. hinder edge is toothed or spiny. Do the 

 scales covering the lateral line differ from those found 

 elsewhere on the body? How? 



In front of the ventral anal fin demonstrate the open- 

 ing of the urinary and the reproductive organs. Dp they 

 Qpen together? • Locate the anus. Is this arrangement 

 typical of tl\g higher or of the lower forms? Do you find 



