Brooks.] 380 [May 18, 



PRELIMINARY REMARKS ON THE STRUCTURE OF THE 

 SIPHON AND FUNNEL OF NAUTILUS POMPILIUS. 



BY HENRY BROOKS. 



The shell of Nautilus pompilius has, besides all the ordinary shell 

 layers, a tube connecting all the air chambers together and open- 

 ing into the living chamber. This tube is the covering of the fleshy 

 siphuncle and will be spoken of as the siphon, as is customary 

 among palaeontologists and conchologists, and this paper is writ- 

 ten to describe its structure in detail. 



The siphon commences in the first chamber as a caecum. The 

 closed end rests against the inner surface of the apex of the shell 

 in a cup-like depression that is generally situated over the scar, 

 but is often found a little on either side of it. This has been ascer- 

 tained b} r examining more than thirty shells of Nautilus pompilius. 

 The siphon consists of a series of tubular sections extending from 

 septum to septum and increasing in diameter as the chambers ex- 

 pand. Each section is made up of two parts, an outer calcareous 

 sheath and an inner tube of conchiolin. The outer sheath extends 

 from the inner surface of a posterior funnel of one septum to and 

 embracing the outer surface of the anterior funnel of the next sep- 

 tum. The inner tube extends from the inner surface of a posterior 

 funnel to the outer edge of an anterior funnel. 



The outer sheath is made up of calcareous spicules overlying 

 one another and arranged in such a way as to form an exceedingly 

 porous structure. Numerous small openings may be seen in its 

 wall with a low power, and a fluid when poured in above any 

 septum rapidly permeates the wall of the sheath and runs clown its 

 outer surface into the chamber below. The spicules are fusiform 

 and as a rule are arranged in stellate figures. There are irregu- 

 lar holes or cavities on the outer surface of the sheaths. These 

 cavities do not extend through the sheaths but are partially closed 

 by the spicules forming the middle portions of the sheaths, which 

 are more closely interlaced than those forming the outer surfaces. 

 The spicules that extend beyond the outer surfaces of the sheaths 

 often terminate in irregular knobs, many of which are covered with 

 slender bristles or spikes, giving the knobs an appearance similar 

 to that of a chestnut burr. Others are hollow at the centre ter- 

 minating in concave discs, made up of slender sticks or bristles 



