MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 137 



The spadix and antispadix do not correspond to any group of tentacles in the female, as far 

 as our present knowledge goes. It has been suggested that they have been formed by the 

 separation of the four ventral tentacles of the superior labial group. It is true that the number 

 of tentiicles comprised by the spadix or the antispadix added to that of the superior labial group 

 equals the number of tentacles in a superior labial gioup of the female, and that in young animals 

 they are like these in size and structure. The innervation of the spadix and antispadix also 

 seems to be like that of the superior labial tentacles. Yet the two organs are so completely 

 separated from the labial tentacles, even standing entirely outside the lal)ial ridge, that we must 

 consider it still an open question if they are represented in the female until embryological 

 evidence can be obtained. 



The ocular tentacles are members of the digital series which have liecome modified for 

 sensory functions. 



This seems the best place to consider another secondary sexual character, which after 

 all is closely connected with the tentacles. Both Vayssiere and Willey point out that a 

 difference exists in the shape of the opening of the male and female shells. In general the shell 

 of the mde is larger than that of the female, and the breadth of the opening of the shell is 

 greater in proportion to its height in the male than in the female shell. But these characters 

 are so variable that in examining a large number of empty shells I was unable to determine 

 which had belonged to males and which to females. Willey himself emphasizes the variability 

 of this character. The hood of the male exceeds that of the female in size in the same manner as 

 has just been mentioned for the opening of the shell. 



The generally larger hood and shell opening of the male seems to be largely the result of 

 the growth of the spadix. 



PALLIAL COMPLEX. 

 MANTLE. 



The mantl-e cavity of Nautilus extends completely around the body, it is shallow dorsally, 

 but ventrally a deep, capacious cavity, which contains the various organs spoken of as the pallial 

 complex. 



The mantle itself is a thin and only slightly muscular fold, which fits closely against the walls 

 of the inhabited chamber of the shell. I wish to make a sharp distinction between the mantle 

 and the body wall, especially between it and the thin, membranous portion of the body wall 

 covering the visceral hump and so frequently spoken of as the mantle. I shall limit the term 

 "mantle" in this description to the projecting fold around the middle of the body, extending for- 

 ward from its junction with the body wall and elsewhere free from the body, surrounding it like 

 a cape. The name can not properly be applied to any other portion of the body wall. 



The ventral and lateral edges of the mantle follow the edge of the shell and are attached to it 

 it (Fig. 1, V M). From umbilicus to umbilicus, dorsally, the mantle forms a free fold, which lies 

 against the involution of the shell (Figs. 1, '2,, and 5, D M). The most shallow parts of the mantle 

 cavity are just beneath the umbilici of the shell, dorsal to each shell muscle. The edge of the 

 mantle following the edge of the shell slopes rapidly upwai'd and backward to the umbilici. 

 The posterior limit of the mantle cavity also slopes upward and somewhat forward to the same 

 point. Thus the depth of the mantle cavity or the width of the mantle, 10 centimeters in the 

 mid-ventral line, is reduced to 1 centimeter over the shell luuscles. The dorsal portion of the 

 mantle is produced upward and forward and is closely pressed against the lower portion of the 

 involution of the shell. In the mid-dorsal line, therefore, the mantle has a width, or the mantle 

 cavity a depth, of about i centimeters. The dorsal part of the mantle cavity contains no organs, 

 and is nearly closed off from the ventral part by the narrowness of the lateral portions, which are 

 still more nearly closed by the upper ends of the crura of the funnel. The dorsal part of the 

 mantle cavity nuist be nearly minimal in volume, since the hood and body wall forming its floor 

 fit closely around the involution of the shell. The dorsal portion of the mantle is probably 

 strongly contracted in alcoholic specimens, since it does not extend nearly as high up on the 



