E. A. L. Sclnvarz — The Aptychus. 455 



solid opposition explanation ; but none can compete with the 

 teaching of the Dundry specimen, and the objections can be very 

 well answered, as I propose to do in the sequel. 



Taking the objections in order : — 



1. Of the many suggestions which have been offered as to the 

 internal nature of the Aptychus, such as the shell of dwarf males 

 residing in the mantle space, like those of some cirrhipedes, or the 

 gizzard teeth, etc., three have gained greater prominence than the 

 rest. The first of these is that put forward by Valenciennes, and 

 recently elaborated by Steinmann,^ namely, that the Aptychus was 

 a structure attached to the funnel, and working like the shells of 

 bivalves by means of ligaments situate along the hinge-line, thus 

 strengthening that organ, and enabling it to eject the water with 

 greater force ; this, then, indicating a higher degree of organism in 

 the funnel than that exhibited by the Nautilus, led Steinmann to the 

 conclusion that tbe Ammonites were Dibranchiata, though, of course, 

 he brings other reasons to bear on the subject ; and from the general 

 acceptance of Steinmann's conclusion, 1 suppose the idea of the 

 Aptychus being a funnel-cartilage has many followers. A second 

 theory is that put forward by Keferstein, Waagen, and von Zittel,^ 

 namely, that the Aptychus was the covering of the nidamental gland, 

 the view being supported by the fact that those glands are usually 

 thrown into ridges, similar to those of the Aptychus, in many recent 

 Cephalopoda. The third is that of von Jhering,^ where, relying 



Fig. 1. Shows the Ammonite animal in the shell in the living resting position. 

 Fig. 2. Shows three stages of the position of the Apytchus after the animal 

 has died. 



upon the fact that the recent sepia has a nuchal cartilage situated at 

 the back of the head, almost identical in shape with some Aptychi, 

 he concludes, therefore, that the function of the Aptychus was to 

 give attachment to the mantle ; and, believing that the Aptychus, 

 as it usually occurs in the living-chamber, retains the position it 

 occupied in life, he concludes that the back of the Ammonite was 

 turned outward, and the funnel internal (endogastric). Although 

 Zittel, in his Paleontology, says that this view seems to have 

 convinced nobody, yet it receives countenance from Haug's con- 

 tention * that some Ammonites must have been endogastric, because 

 the bay in the outline of the aperture, which was supposed to lodge 

 the siphon, is internal in some genera. 



1 Steinmann, Berich. natm-forsch. Gesell., Freiberg, vol. iv. pt. 3, 1889. 

 ^ Von Zittel, Handbuch der Palseontologie : Cephalopoda. 



2 Neues Jahrbuch, 1881, pt. i. p. 80. 



■• Gattung Marpoceras, Neues Jahrbuch, 1885, pt. iii. p. 596. 



