348 PROFESSOE RAY LANKESTER AND A. Q. BOURNE. 



shown in the diagram (fig. 4), the relations of these parts in the 

 male is (as in the female) such as to leave little doubt that we 

 have in them a rudimentary condition of the left spermatic 

 duct and its external opening. Whether the pyriform append- 

 age in any way rej)resents also a rudimentary testis, must 

 remain for the present uncertain. 



The significance of the occurrence of paired genital ducts in 

 Nautilus is not so great as it would he were it not the fact that 

 both in the Octopoda and in Ommastrephes among Decapoda, 

 the female genital ducts are paired, and both equally well de- 

 veloped, although the sperm-duct of the males is (with the 

 solitary exception of El e done moschata, recorded by Kefer- 

 stein) single. 



The single oviduct of those Cephalopoda which have but 

 one, and the single sperm-duct also, is, in all cases, that of the 

 left side; whilst in Nautilus the right oviduct and the right 

 spermduct is large and functional, the left being that which is 

 rudimentary. 



Nevertheless, on account of its archaic character, and of the 

 great significance of the primitive Cephalopod structure in re- 

 lation to the morphology of Mollusca generally, any divergence 

 in Nautilus from the condition obtaining in other forms has 

 possibly and even probably a special significance. Such 

 divergence may be the remnant of an ancestral condition, and 

 in so archaic a form as Nautilus, is not readily to be dis- 

 missed as "an adaptation" pectiliar to that form. 



Hence the doubt which might have arisen through Nautilus 

 as to the primitive arrangement of the molluscan genital ducts 

 is removed. They are now shown to be paired ducts, as in 

 Chiton, and as in Lamellibranchs. 



