CONTACT ORGANS IN KILLIFISHES OF WOODS HOLE. 179 



TABLE III. 



(F. majalis males collected May 14, 1907.) 



No. of Specimens. Distribution of Contact Organs. 



2 Fairly numerous on the cheeks. 



4 On cheeks, top of head, and around eyes. 



5 On cheeks, top of head, around eyes, and a few rudiments 



on the body zone between dorsal and anal fins. 



I Rudiments on cheeks and around the eyes, a few on the tips 



of the anterior rays of the dorsal fin. 



I Fairly numerous on cheeks and around the eyes, scattering 



on top of head, a few on the dorsal fin, and numerous on 

 the body zone between the dorsal and anal fin. 



I Numerous on cheeks and around the eyes, scattering on top 



of the head, numerous on body zone between the dorsal 

 and anal fins, and on the distal portions of nearly all of 

 the rays of the dorsal fin, and a few on the posterior lobe 

 of the anal fin near the tips of the rays. 



The order of appearance of the organs in the various regions 

 seems to be about as follows: (i) On cheeks and around the 

 eyes, (2) on top of head, (3) on the body zone between the 

 dorsal and anal fin, (4) on the dorsal fin, (5) on the anal fin. 



Any attempt to correlate this order of appearance with the 

 relative functional importance of the organs in the different regions 

 meets at once with serious difficulties. It can hardly be sup- 

 posed that the organs in the head region are of more importance 

 as spawning accessories than are those on the dorsal fin. The 

 fact, however, that the organs on the head are used in the pre- 

 liminary phases of spawning, such as courtship and rivalry, 

 might better account for their early appearance. Thus the factor 

 of priority of functioning might be conceived of as outweighing 

 functional importance. In F. heteroclitus, however, the opposite 

 condition seems to prevail. The difference may lie in the fact 

 that, in F. heteroclitus the importance of the fins as claspers is 

 much more pronounced than in F. majalis. 



The order of appearance of the individual contact organs on 

 the fin rays has been referred to. They appear first on the dis- 

 tal portion of each ray, but, as the ray increases in length, those 

 first formed are separated farther and farther from the tip of the 

 ray. Later they appear proximal to those that were first formed. 



On the scales the first organ to appear is always located in the 

 center of the exposed arc of the scale. Many specimens of both 



