REPORT ON THE PENNATULIDA. 123 



of the length of the rachis above its commencement, from 

 which point they diminish gradually in length towards the upper 

 end of the rachis, and much more rapidly towards the lower end. The 

 number of polypes composing the leaves varies according to the length 

 of the leaf ; the greatest number, found in the longest leaves, being 

 twelve in the female specimen (Fig. 8 d), and in the male fifteen ; while 

 the topmost leaves consist of three or even only two polypes each. 



The rachis and leaves are of a deep red colour, due, not to the 

 fleshy body-substance which is nearly colourless, but to I'ed calcareous 

 spicules which are present in immense numbers throughout these 

 portions of the Pen (Figs. H, -i, and o /). The stalk is much paler, the 

 spicules in it being colourless. 



Anatomical Description. 

 1. — The Stalk and liachin — 



Thestalk (Figs. 1, 2, 3) which forms about 2-5thsof the entire length 

 of the Pen, is cylindrical, with a diameter, in the female specimen, of 

 0-21in. along the gre iter pai-t of its length. The bottom third is 

 somewhat dil;i/ted and bulbous, and the upper end, just at the junction 

 of stalk and rachis, slightly constricted, forming as in Fnniculhui. 

 the uari-owest portion uf the stalk. 



As the Oban specimens were destined for museum purposes, we 

 have been unable to investigate the structure of the stalk in them, and 

 the following account is based on a series of preparations made from 

 a couple of specimens in the Owens College Museum, obtained from 

 Naples. 



The stalk is really a tube, being traversed along its whole length 

 by an axial canal, whose diameter along the greater part of the length 

 is about i that of the stalk itself, somewhat exceeding this in the upper 

 and lower thirds, and being rather smaller in the middle third. At 

 the bottom of the stalk this canal is said by Kolliker to open to the 

 exterior by a minute orifice, the existence of which we have, however, 

 been unable to confirm. 



The central canal is divided into two along the whole length of the 

 stalk by a longitudinal partition ; and in the upper half of the stalk, 

 owing to the presence of two other partitions, into four, whereof one 

 is dorsal, one ventral, and two lateral. 



The walls of the stalk present the following structure : — On 

 the outer surface is an epidermis, which, although of some thickness, 

 consists of only a single layer of closely-packed columnar cells. 

 Beneath this is a thick connective-tissue layer, or dermis, forming 

 from 3 to ^ the total thickness of the wall. Imbedded in this dermis 

 are an immense number of calcareous spicules crossing one another at 

 every conceivable angle, and set so closely together that in many 

 places the connective tissue matrix is completely concealed by them. 

 These spicules which, unlike the spicules of the rachis and leaves, are 

 colourless, have an average length of O'OlHin., and width of 0-OOlin., 

 the total thickness of the dermis, to which they give considerable 

 strength and toughness, being aliout O-OlOin. 



