176 H. H. NEWMAN. 



be effective in enabling the male to hold the female more securely. 

 In some specimens of F. majalis the organs are restricted to the 

 small posterior lobe. From the few observations made thus far 

 on the spawning attitude of this species it would seem that in 

 many cases the anal fin can play only a minor part in clasping. 

 Hence it may be that there is at present a tendency to reduce 

 the number of organs on this fin. The writer takes occasion to 

 point out this weak spot in the evidence in favor of the general 

 conclusion that the distribution of contact organs is intimately 

 correlated with the spawning attitude. The possible explanation 

 may lie in the fact that only a very few observations have been 

 made of spawning in this species, and the attitudes then seen may 

 depart somewhat from those assumed in the open. All observa- 



FIG. 10. Camera drawing (X I2 ) f ^ le distal portion of a single ray from the 

 posterior lobe of the anal fin of a spawning male F. majalis. The solid black repre- 

 sents the osseous structure of fin ray and contact organs, the single line the boundary 

 of the epidermal portions. 



tions agree, however, as to the promiscuity of the spawning. In 

 both F. heteroclitus and Cyprinodon variegatus, in which all of the 

 details of the spawning attitude have been accurately determined, 

 the correlation between spawning attitude and distribution of the 

 contact organs holds without exception. The relationship of the 

 organs to the fin rays is the same, with minor differences, in all 

 species studied. 



Structure. - - Attempts to section the contact organs were dis- 

 appointing. After complete decalcification there still remained 

 in the central supporting spikes crystals of some hard substance, 

 probably guanin, that resisted the knife edge and tore through 

 the section. Fragments of tissue from such sections revealed 

 the fact that the epidermal covering was thin and of the usual 

 type and that the dermal layer was much thicker and was com- 

 posed of rather loosely arranged connective tissue, blood vessels 

 and a few nerve fibers. A substitute method was found, how- 



