The Oviposition of Nautilus macrornphalus. 471 



Fia. 6. The inner capsule of the same egg, seen from below (i.e., from the side 

 directed towards the surface of attachment). Half the lower wall of the 

 capsule has been removed by slitting along one of the lateral sutures, and 

 along the median groove (mentioned in the text), to show the brown-coloured 

 vitellus lying in the capsule. The continuity of the lateral sutures (I. s.) in 

 front is well seen. The shaded area represents a depression which occurred in 

 the wall of the inner capsule in the region of the area of attachment of the 

 outer capsule. 



the lower surface of the vitellus in an egg which had been allowed to 

 develop for twenty-four hours after being first seen. The large quan- 

 tity of yolk points to the occurrence of a long period of incubation. 



Sometimes the capsules of the egg are malformed, and, on opening 

 such an egg, the vitellus is found to be already ruptured. 



From the fact that in New Britain I obtained mature males of 

 Nautilus pompilius, carrying a spermatophore in the cephalic region 

 throughout the year, I came to the conclusion that the reproduction 

 of Nautilus took place all the year round. It now seems probable 

 that the breeding of Nautilus, as of so many other forms, is subject 

 to a definite law of periodicity. 



Finally, it may be mentioned that N. macromphalus varies with 

 regard to the position of the spadix on the right or left side, and 

 also as to the origin of the siphuncular artery, in the same way as 

 N. pompilius does. The male of N. macromphalus carries a spermato- 

 phore in the same position as in N. pompilius ; and, in fact, the only 

 essential difference between the two species that I know of at present, 

 is the difference between the shells in the umbilical region. 



