POINTS TO NOTE 315 



changes of venue and gear in native fishing operations, 

 and of the kinds of fish brought to market, will often 

 afford useful information. 



Among shore fishes, the observations of breeding 

 habits, to which allusion will be made later, is often 

 both easy and interesting ; and, at whatever depth a 

 fish is captured, sexual differences of form or colour 

 may be observed and noted by comparison of examples 

 of both sexes, especially such as are shown by their 

 roes or milt to be approaching the breeding season. 



As an observation of such sexual differences is of the 

 greatest importance to systematists, and can best be 

 made in a living or fresh example, we may briefly point 

 out the details which demand attention : 



1. The presence of external copulatory appendages 

 (as in sharks, rays, and chimaeroids), or of a prominent 

 genital papilla. 



2. Outgrowths of the scales or dermal covering, and 

 differences in the teeth. 



3. Differences in the profile of the head and back. 



4. Elongated fin rays (especially of the dorsal and 

 anal fins). 



5. Thickening of the rays of the pectoral, ventral, 

 or anal fins. 



6. Differences in size. 



7. Differences in coloration. 



8. Differences in the arrangement of the luminous 

 organs of oceanic fishes. 



Attention should further be paid to the size at which 

 each sex commences breeding, to the comparative 

 abundance of specimens of the two sexes, and to the 

 permanent or transitory nature of the sexual differences 

 observed. 



In many fishes colour changes may occur with 

 startling rapidity, especially under the influences 



