REPORT OF THE STATE PALEONTOLOGIST I9O3 319 



After the formation of several cameras the animal began to 

 withdraw also from the apical conch and then the formation of 

 the endosiphosheaths set in, which continued throughout the 

 neanic or adolescent age. Bather has described this process so 

 graphically [1894, p.433] that we can do no better than quote 

 here from him. 



We know that in Nautilus and Spirula after the secretion of 

 the septal necks, the outer coat of the siphuncle, both inside and 

 outside the region of the septal neck, becomes hardened by cal- 

 cium carbonate; this gives it a certain rigidity and assists its 

 retention in the fossil state. The same thing must have occurred 

 in the coat of the visceral cone. Now in Piloceras, when the 

 animal advanced in the shell its viscera naturally followed it, and 

 by suction the walls of the visceral cone were drawn in so as to 

 form the narrow and empty siphuncle. At least such would 

 have been the case had not the stiffness of the outer coat pre- 

 vented complete yielding of the skin, especially at the posterior 

 part where the siphuncle tended to begin, but where the coat 

 was most calcified. It must therefore have happened that the 

 inner layers of the skin were gradually torn away from the outer 

 layers. Another stiffening of the skin would take place higher 

 up and the process would be repeated. 



As an explanation of this periodical sloughing it is suggested 

 that the actual moment of the casting "was after the emission 

 of the generative products, when the visceral cone was flaccid ; 

 this explanation coincides with Seeley's explanation of the origin 

 of septation itself, but it is not exposed to the objections brought 

 against the latter." 



Perhaps the fact that the cast of the visceral cone preserved 

 by the mud filling of the '' Spiess " within the last endosipho- 

 sheath is sometimes of an undulating character, as in the speci- 

 men reproduced in plate 8, figure 3, and at other times well expanded 

 and smooth, thus indicating considerable difference in the rela- 

 tive tension of the wall of the visceral cone, can also be taken 

 to point to the conclusion that the visceral cone, which in our 

 form undoubtedly expanded far back into the siphuncular tube, 



