194 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



there is sonic reason to consider as sensory. This portion of the segment is also provided with a 

 peculiar musculature which enables it to act as an adhesive organ of considerable power. 



The evidence renders it probable that the lamellated organ upon the inferior labial lobe of 

 the female is composed of a number of modified cirri. Between the lamella? are peculiar pits, 

 lined by an epithelium which seems to be sensory. 



Van dee Hoeven's organ of the male is shown to be the homologue of the inferior labial 

 lobe of the female. Its lamelhe correspond to the lamelhe and cirri of the inferior labial lobe. 

 Van der Hoeven's organ is largely glandular; its activity may be periodic. Among the gland 

 cells in all parts of the organ are scattered great numbers of sensory cells of a peculiar character. 

 These seem to correspond to the sensory cells observed upon the inferior labial lobe of the 

 female. It is to be noted, however, that in the latter organ the sensory cells are concentrated, 

 but in the former scattered. The inferior labial lobe is provided with a quite complex special 

 musculature. A similar musculature is possessed by Van dee Hoeven's organ. 



The second cirrus of the spadix bears a set of "lands hitherto undescribed. The structure 

 of the large slime gland upon the outer .surface of the spadix sheath is described. A similar 

 gland is found in a less developed condition upon the outer side of the sheath of the antispadix. 

 The spadix possesses a powerful muscle, extending from its base across the cephalic sheath. 



The ocular tentacles are proven by their innervation to be members of the digital series, modified 

 for a sensory function. Upon the, inner side of the nerve, within the ocular tentacles, is an acces- 

 sory nerve composed of many bundles of nerve fibers, which enter the primary nerve as they pass 

 toward the central nervous system. The ocular tentacles possess " breaking planes." i. e., planes 

 where the tissues are somewhat discontinuous, and along which the tentacles break with great ease. 



Attention is called to the fact that the position of the organs of the pallia! complex of Nautilus 

 has been incorrectly figured and described by all authors except Joubin. The arrangement of 

 these organs differs from that found in the Dibranchiata, and approaches that found in many 

 Gastropoda. The gills, anus, preanal and interbranchial papillae, pericardial and renal pores. 

 and the nidamental gland are situated upon the inner surface of the mantle. The paired repro- 

 ductive orifices are situated upon the body wall within the mantle cavity. 



There does not yet seem to lie sufficient evidence to warrant our calling certain papilla? near 

 the bases of the gills osphradia. Both dissections and serial sections of the papillae in question 

 have failed to show the special innervation required; other observers also seem to be a little less 

 than sure of the presence of special nerves to these papilla?. 



The funnel is composed of two essentially different portions, the anterior part being fibrous, 

 the posterior portion muscular. The crura of the funnel are so formed that they can, by a 

 fanning motion, cause respiratory currents through the mantle chamber, and possibly currents 

 strong enough for the progression of the animal. 



The visceral portion of the body wall is thin and non-muscular. It contains a nervous plexus. 

 It is attached to the shell by three aponeurotic bands proceeding from the ends of the shell 

 muscles. The dorsal and posterior ventral bands limit the septum-forming portion of the body 

 wall. A sharp backward projection of the dorsal aponeurotic, band corresponds to a depression 

 in the face of each septum in the younger half or two-thirds of the shell. 



Aside from minor additions in the description of the anatomy of the digestive tract as a whole, 

 the muscles of the buccal mass are described and figured. They are found to form a quite highly 

 developed .system. 



The renal organs are found within the mantle and in the reverse position from that described 

 by earlier authors. 



Willey's sketches and my own dissections have been combined to form a nearly complete 

 account of the arterial circulation. 



Some previously undescribed nerves have been followed to their terminations, especially the 

 nerves of the ocular tentacles, of Van deb Hoeven's organ, and of the spadix and antispadix. 



The ocular nerves arc branches of a nerve supplying digital tentacles as well. The nerves of 

 Van dee Hoeven's organ correspond to the nerves of the inferior labial lobe in all particulars. 

 The otoevstic nerve arises from the cerebral ganglion. 



