122 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



cles are more or less crowded to the outside of the row formed by the other six, as is shown in 

 Text-fig. 4, and in Fig. 7, SLL. Aside from these there are no differences between the superior 

 labial lobes and tentacles of the two sexes. 



Each cirrus possesses a nerve, which springs directly from the pedal ganglion. These 

 nerves leave the edge of the ganglion just dorsally to the nerves of the digital tentacles; being 

 of only about half the size of the latter they are easily distinguished from them, although not so 

 readily traced to their respective cirri. 



SPADIX AND ANTISPADIX. 



The spadix and the antispadix are morphologically equivalent organs, although the anti- 

 spadix is simple in all its parts, while the parts of the spadix are highly developed and modified, 

 and several structures are there developed which are not represented in the antispadix. A 

 previous study of the antispadix will probably aid in the understanding of the spadix. 



Before proceeding, we must notice the position of the two organs. The spadix is usually 

 upon the left side of the head and the antispadix upon the right side, but this arrangement may 

 be reversed. Out of forty-seven male Nautili, nine, or 19 per cent, had the spadix upon the 

 right and the antispadix upon the left side. Willey found an even greater proportion of 

 reversals. "Out of thirty-seven males which were examined ad hoc. twenty-three had the 

 spadix upon the left side and fourteen had it upon the right side" (1896, 1)). This is 37 per cent 

 of the total. 



One of my specimens possessed a well-developed spadix upon one side and an abnormally 

 developed spadix upon the opposite side. 



The antispadix is composed of four tentacles similar to those of the superior labial groups, 

 except as they are somewhat larger and longer than the latter. (Fig. 7, A. Sp; Fig. 12.) The 

 tentacles arc arranged in a row, which in the natural position of the animal is dorso-ventral. 

 To distinguish the tentacles I shall number them 1, 2, 3, 4-, from above downward, and shall 

 speak of them as the first, second, third, or fourth tentacles. The sheaths of the first, second, 

 and third tentacles are fused as far as their tips, thus forming a narrow, flattened process. It is 

 convenient to speak of the fused sheaths as the sheath of the antispadix. The fourth tentacle 

 is united to the process at the base only. (Fig. 12.) It is situated a little externally to the other 

 tentacles, extending past the third, so that its dorsal edge comes to lie in a groove formed by a 

 projection of the sheath of the antispadix. 



At the bases of the cirri the muscular tissues of the cirri and their sheaths unite to form a 

 strong, flat sheet of muscle, which lies against the inner side of the cephalic sheath, but entirely 

 separate from it until near the cartilage. Here it unites with the tissues of the cephalic sheath. 

 The muscular base of the antispadix is entirely separate from the muscular base of the superior 

 labial lobe, although close to it. It is easily seen when the skin between the antispadix and the 

 buccal mass has been cut. 



Upon the outer surface of the sheath of the antispadix, near its tip and between the first 

 and second cirri, is a small glandular area. (Fig. 12, Gr.) Its structure will be described with 

 that of a similar area upon the sheath of the spadix. 



The antispadix projects from a pocket between the cephalic sheath and the ridge of the labial 

 lobe and at the ventral end of the lobe. (Fig. 7; Text-fig. 4. ) The lobe of the antispadix is about 

 two centimeters in length from the base of the pocket to the tip of the sheath. As a consequence 

 of the shortening of the rows, the superior labial tentacles are further removed from the ven- 

 tral side of the cephalic sheath in the male than in the female. (Text-tigs. 2 and 4.) The low 

 ventral portions of the labial ridge are therefore considerably increased in length in the male. 

 As the spadix increases in size it crowds the superior labial tentacles of this side still farther 

 toward the dorsal side of the head and stretches the ventral portion of the labial ridge. 



The spadix presents a very different appearance from the antispadix upon the opposite side of 

 the head. (Fig. 7, Sp. ; Figs. 13 and 14; Text-fig. 4, S.) It forms a large, very solid organ, five 

 to seven centimeters in length, two to three centimeters in dorsi-ventral measurement, and one 



