MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 1 ( .»."> 



frequently cases of the twinning of two or more crystals arc seen. In instances where two crys 

 tals are twinned the angle between their axis is usually 78 , any divergence from this angle being 

 quite small, so far as observed. When twinned the ends of each crystal are as perfect as in 

 single crystals. The union of two or several crystals forms the cross and star-shaped bodies, 

 "etc." mentioned by Macdonald. 



CARTILAGE. I Fig. 40. ) 



In the region of the bases of the digital tentacles is a large and strong cartilage which affords 

 a firm place of attachment for the major muscles of the body. It is composed of a central por- 

 tion which Owen has termed the body, from each side of which a pair of processes project 

 dorsally (the cephalic processes) and ventrally (the infundibular processes). The cartilage slants 

 from above downward and forward, the ends of the cephalic processes reaching dorsally to 



the body wall of the nuchal region immediately back of the h 1 and in front of the crura of 



the funnel, while the infundibular processes extend into the funnel through the inner wall of 

 which they show as white lines. 



The greatest width of the cartilage is .". centimeters, the length between the tips of the proc- 

 esses is 4.75 centimeters. The infundibular processes have a length of 2.5 centimeters, the 

 cephalic processes a length of 1 centimeter. 



The cephalic processes are round and end squarely. The muscles of the digital tentacles, 

 the labial tentacles, and the spadix are attached to their anterior faces. The shell muscles find 

 an attachment upon their posterior faces. 



The infundibular processes are much broader than the cephalic as well as thinner and nearly 

 Hat. Their broad anterior faces are turned .somewhat inward as well as upward. These faces 

 are slightly concave, while the outer and posterior faces are slightly convex. The tissues of 

 the anterior portion of the funnel are attached to the lower portion of the anterior faces, while 

 the muscles of the posterior portion and of the crura of the funnel are attached to the posterior 

 faces of the infundibular processes. The pedal ganglia lie against the upper portions of the 

 anterior faces of the infundibular processes, while the pleurovisceral ganglia are supported by 

 the median processes of the body of the cartilage. The body of the cartilage is bent downward 

 and backward in the middle, forming a sharp reentrant angle anteriorly and a projecting point 

 posteriorly. From the upper portions of the anterior side of the body of the cartilage a pair of 

 small processes project toward the median line, the median processes (m. p.). The muscles of 

 the buccal mass, the inferior labial lobe or Van der Hokyen's organ, and the levator muscles 

 of the funnel, are attached to the body of the cartilage. The points of attachment of the latter 

 muscles are marked by the dotted lines at 1. i. in Fig. 40. 



The body of the cartilage is penetrated by two veins on each side. These enter widely sep- 

 arated upon the anterior side, but leave the cartilage close together upon the posterior side, the 

 cavities of the cartilage containing the veins opening here into a common depression. The upper 

 veins (v) come from the region of the base of the tentacles: the lower veins (v') come from the 

 anterior portion of the funnel. In the central part of the cephalic process is a small cavity 

 which extends nearly to its tip and communicates with the cavity containing the vein from the 

 cephalic region. 



SUMMARY. 



It may be a convenience if the additions to our knowledge of the anatomy of NomtUus 

 pompUms presented in the foregoing pages are briefly summarized. The principal result aimed 

 at has been to unite the numerous isolated observations on Nautilus in a coherent account which 

 will at least have the advantage of accessibility. 



It has been found that the digital tentacles have a regular arrangement, few variations from 

 which exist. 



The nerve of each tentacle possesses accumulations of ganglion cells about its periphery 

 corresponding to each of the annulations of the outer portion of the tentacle. The inner pro- 

 jecting side of each segment of the digital tentacles is covered by a peculiar epithelium, which 



