334 ^^EW YORK STATE MUSEUM 



while the dorsal one is very convex, or in other words, that the 

 ventral side appears as a base, all growth taking place in dorsal direc- 

 tion, tends also to support the view that the conch was carried slightly 

 oblique and at rest placed in a horizontal position. 



It is interesting to note in this connection the views 

 held by prominent zoologists as to the polarity of the 

 Cephalopoda. Huxley, Lancaster and Lang give the 

 original cephalopod the position shown in the diagram- 

 matic figure reproduced here from Lancaster, while Ver- 

 gramoPorigin- ^"^^^ holds that the antcro-posterior axis of the cephalopod 

 (Co'py Vr^om is showu by foHiis as Loligo at rest [see fig.24]. It 



Lancaster) 



seems that the structure of Piloceras explan- 

 a t o r , which both in organization and the time of its appearance 

 is to be considered as a primitive form, could be easily reconciled with 

 this latter view, if we assume 

 that it was a sluggish creeping 

 form which would rest its shell 

 on the flat ventral side, but lift 



it up slightly while moving. ^^^-^ LoUgoatrest. (Copy from Verrill) 



Endosiphocoleon. It remains to us to trace the development of 

 the endosiphocoleon of the siphuncle of Piloceras ex- 

 plan a t o r, which can be best done by reference to the series 

 of sections 1-7 on plate 11. 



AVe have already stated that the endosiphocone becomes flatter 

 as it approaches its posterior end till at its termination it is five 

 or more times as broad as high [see pi. 13, fig.2]. From this end 

 proceeds the endosiphocoleon, a flat sheathlike canal, which is nearly 

 as wide as the innermost endosiphosheath ; in section i by a sec- 

 ondary fracture apparently still wider. The longitudinal section 

 [pi. 13, fig.3] shows this endosiphocoleon in a young specimen, cut 

 through its shorter axis. It demonstrates that the endosipho- 

 coleon possesses a thin conch iolinous wall which extends through 

 the last endosiphosheath into the cavity of the endosiphocone ; 

 and hence was here not formed as a continuation of the external 

 conchiolinous layer of the endosiphosheath, but within the apical end 



