326 H. H. NEWMAN. 



is probably an index of a very rapid metabolism that expresses 

 itself in other ways such as greater activity, greater courage, 

 and in the production of excrescences, etc. 



2. The thickening of the anal fin in the female may be partially a 

 phenomenon of inflammation produced by irritation. The sources 

 of irritation are twofold. In the first place the tip of the fin is 

 rubbed violently against the bottom during the spawning act. In 

 the second place the frequent expulsion of eggs through the tub- 

 ular extension of the oviduct that runs down the posterior ray of 

 the fin, probably causes inflammation in this and adjacent parts. 

 The thickening of the fin gives a firmer support for the spawning 

 pair than would the fin in its usual condition, and in addition 

 stirs up the mud more effectively as has been shown. 



3. The steely blue gleam so characteristic of spawning males, 

 reminds one of iridescence but is not of the same character. The 

 blue color is probably due to a combination of chromatophores 

 and iridicytes. The former are extremely extensible in that the 

 pigment is capable of flowing out over a wide area through slen- 

 der, branching canals. The latter are extremely minute prismatic 

 crystaline bodies that serve the purpose of refracting the light. 

 They evidently lie above the chromatophores which furnish the 

 absorbing background. In some way the colors at the red end 

 of the spectrum are absorbed by the melanin and the combined 

 colors of the violet end of the spectrum are reflected as the steely 

 blue gleam. The extension and contraction of the melanophores 

 seems to be a reflex closely associated with sexual excitement, 

 and may be considered as a sort of involuntary flush. 



4. The structures that I have chosen to designate as contact 

 organs, occur as finger-like processes on the margins of all the 

 scales in certain regions, and upon the fins that are used in clasp- 

 ing. The appearance of these processes is well shown in the 

 photographs reproduced in Text Plate III. 



It is of interest to note that contact organs occur only on 

 actively spawning males and only upon those parts that are in 

 contact with the female during the spawning act and upon the top 

 and sides of the head, parts that are used for butting the female 

 in courtship and one another when fighting. The distribution of 

 the contact organs in the four species studied is represented in 



