MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 171 



surface during the whole time of observation. They did not go far in one steady direction, hut 

 tended to go in circles, as in fact did another one whose siphuncle was uncut. It' one of the 

 individuals floating at the surface was forced down to the hottoni with a hand net, it would 

 slowly rise to the surface again. This also often happens with a Nautilus that has not been 

 operated on. 



•'The results indicated by the above experiments, which, it may be added, are worth 

 repeating, may be summarized as follows: 



•"The cutting of the siphuncle (a) does not temporarily affect the vitality of the animal; (/?) 

 does not prevent it from making movements of translation; 1 (y) does not prevent it from floating 

 at the surface; (8) does not prevent it from sinking to the bottom. 



"It still remains to be ascertained whether a Nautilus whose siphuncle has been cut, having 

 sunk to the bottom of the sea in shallow water, will undertake a journey to the surface. My 

 experiment of July 10 would seem to indicate that this might be expected to occur. 



'"The above experiments do not appear to oppose the view which I expressed in a former 

 communication — that the siphuncle of JYautiht* junnpiliux is, in some measure, of the nature of 

 a vestigial structure. 



"It might, indeed, be legitimate to suppose, on the principle of the correlation of organs, 

 that in the Nautiloidea the course of evolution has led to a reduction of the siphuncle pari passu 

 with an increase in the efficiency of the chambers as hydrostatic organs." 



REPRODUCTIVE SYSTEM. 



The first specimens of Nautilus to be obtained were females. After Van dee Hoeven had 

 received a male specimen for many years again only females were obtained by naturalists, until 

 the opinion came to be held that the females of Nautilus must greatly exceed the males in num- 

 ber. In recent years, however, especially in the collections made by Willey and in the Menage 

 collection, the ratio has been inverted, the males being about three times as numerous as the 

 females. 



Willey states, in Natural Science for dune, 1895, that out of sixty-seven individuals, fifty- 

 one were male and sixteen female. In the Menage collection out of sixty-six specimens fifty 

 were males and sixteen females. These numbers do not justify us in yet stating that there is a 

 difference in the numbers of the sexes. The males may be much the more active in their habits 

 at all times; the females may also retire into hiding during oviposition, and may possibly remain 

 watching over their eggs until the young hatch, so that during a large portion of the year they 

 are less liable to capture than are the males. 



REPRODUCTIVE ORGANS OF THE MALE. (FlG. 38.) 



The testis is a large oval organ situated in the extreme posterior and upper part of the ccelom, 

 directly beneath the origin of the siphuncle (Figs. 7 and 38). Its posterior face is smoothly 

 convex, fitting the concavity of the septum. The anterior surface, however, is flattened and 

 shows irregular facets caused by pressure against other viscera, the stomach and liver upon the 

 left, the intestine and the accessory reproductive gland upon the right. 



The testis is covered by an extremely thin, delicate tunic, through which may be seen the 

 indistinctly demarcated lobes of the organ. Over the posterior surface the tunic is closely 

 attached to the tissues within, connective tissue strands extending from the tunic between the 

 lobes. Anteriorly the tunic is entirely free from the mass of inclosed tissue, forming a sac 

 which opens through a slit at the end of a short funnel-shaped production of the tunic (Fig. 

 38,T.ap.). 



The testis does not lie free within the ccelom, but is attached to its walls by several liga- 

 ments. The case is summed up shortly by saying that the testis is contained within a ligament 

 which has been invaginated into itself at one point to form the cavity of the testis. The point of 

 invagination corresponds to the opening of the testis. This genital ligament (Fig. 38, g. 1.), as 



1 In speaking above of progressive movements I mean, of course, in the usual backward direction. 



