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W. J. CROZIER 



animal endeavoring to mate with a large one, but such attempts 

 are not as a rule successful. In special situations this process of 

 ' equalization' of sizes may be effective, but it is not of primary 

 importance. 



Nor, as a rule, are the movements of the elevated genital pa- 

 pilla effective in 'equalizing' the size of two nudibranchs. Dur- 

 ing the close approach of two specimens which are attempting 

 to copulate their papillae are considerably protruded. In the 

 center of each papilla is the opening which communicates with 



6 7 8 S )0 Jl 12 )5 K )5 16 IT cms. 

 Tcta/ /encf/^. 



Fig. 20 Showing the relation (A) between total length and distance of genital 

 papilla from mouth; and {B) between total length and height of the papilla 

 above ventral surface of the foot, in creeping. 



the sperm-receptacle and seminal duct. The surface of the 

 papilla apparently corresponds to the inner surface of the ' genital 

 atrium' of Smallwood and Clark ('12), who give a diagrammatic 

 figure of the reproductive apparatus in this species. As the 

 two papillae are brought nearer and nearer together, they be- 

 come still further enlarged, and when their tips come into con- 

 tact the movements of the animals as a whole cease. A slow 

 pulsatile motion of extension and retraction is now, evidenced 

 by each papilla, the movements being reciprocal and the two 

 papillae remaining closely pressed together. If two individuals 

 in this condition are separated by a slight displacement of one of 

 them with a glass rod, the genital papillae become widely pro- 

 truded, and are usually quickly successful in returning to their 



