10 PHYSIOLOGICAL SERIES. 



The following specimens illustrate the modifications of the 

 central supporting axis in the Gorgonacea (Axifera of Gray). 

 The crust outside the axis always contains numerous spicules. 



Kolliker, Icones Histologicae, Zweite Abtheilung, 1865. 



G. v. Koch, Morph. Jahrb., Bd. iv. 1878, p. 447. 



Axis containing coelenteric canals. 



A. 29. Small piece of Paragorgia arborea, and two transverse 

 sections. The axis is not well defined ; it consists mainly 

 of firm mesogloea with some spicules, and is traversed by 

 coelenteric canals. The spicules are most abundant near 

 the surface of the axis, and in the mid spaces between the 

 canals. The extended polyps may be seen on the surface of 

 the specimen. The entire colony is branched mostly on one 

 plane, and is often 1'5 or 1*8 metres in height, with diameter 

 at base of 15 to 20 cm. Presented by Prof. C. Stewart. 



A. 30. Portions of Paragorgia arborea } with diagram and draw- 

 ings of its structure. PI. IV. fig. 2. 



Presented by Prof. C. Steicart. 



Axis formed by fused spicules and containing 

 ccelenteric canals. 



A. 31. Portions of Melitodes ocliracea, and drawings of its struc- 

 ture. The axis is jointed, consisting of short thickened 

 nodes composed of loosely arranged spicules united to one 

 another by their extremities ; the internodes are of a darker 

 colour, containing more inorganic matter and with densely 

 crowded and fused spicules. The spicules of the axis differ 

 in form from those of the crust, but amongst them are 

 occasionally found some of the crust-spicules that have 

 been extruded from that structure. The axis is traversed 

 by coelenteric canals. PI. V. fig. 1. 



Presented by Prof. C. Stewart. 



Axis solid, and secreted by a layer of special ectodermic 

 cells (calycoblasts). 



A. 32. Suberogorgia suberosa, with drawings of its structure. 

 The axis is composed of colourless spicules and horny 



