300 ROBERT PAYNE BIGELOW. 



Therefore it was decided to make a fresh examination of the fin 

 structure in the adults of the three local species, and a thorough 

 search of the literature on this subject. The results of this 

 investigation are given in the present paper. 



The divergence of the present results from those obtained by 

 previous investigators may be due to the difficulties of obser- 

 vation. The fin-rays of Fundulus are all of the soft kind. Each 

 ray consists of two parallel columns of segments bilaterally 

 arranged. In the anal fin the first and last of the rays are 

 unbranched. The other rays are branched dichotomously, one 

 half to one third of the distance from the base, and usually the 

 longer branches are bifurcated again. In both the dorsal and the 

 anal fins the ray bordering the posterior margin is frequently very 

 slender and easily overlooked. In some specimens there are two 

 very slender posterior rays closely united at the base. 



In preserved specimens that have been hardened with the fins 

 flexed, the folding of the fin makes it very difficult to observe the 

 posterior rays. In the present investigation observations were 

 made with a binocular microscope and transmitted light. Some 

 of the specimens were examined while fresh. Most of them were 

 killed and preserved in 5 per cent, neutral formalin in sea water, 

 after being anaesthetized by a few crystals of chloral hydrate 

 inserted in the mouth. The specimens to be killed were placed in 

 the formalin one at a time and the dorsal and anal fins were 

 quickly grasped with forceps and held in an extended position 

 until sufficiently hardened. In order that the specimens should 

 lie flat in the dish during the remainder of the hardening process, 

 the air-bladder was punctured by an incision in the body-wall just 

 above the tip of the pectoral fin and parallel to its dorsal edge. 

 By this method specimens were preserved with the dorsal and 

 anal fins in the best posture for observation. 



In the transparent fins of F. diaphanus prepared in this way 

 and viewed with the binocular microscope, it was easy to count the 

 fin-rays when illuminated by transmitted light. In the two other 

 species pigmentation of the fin often obscured the rays. This is 

 especially true of the densely pigmented dorsal fin of F. hetero- 

 clitus, on which it was at times necessary to use a dissecting 

 needle. 



