ENDOSKELETON. ANIMALS. 13 



the visceral disc is stiffened by minute disc-shaped spicules 

 often perforated in the centre. 



Presented by Prof. C. Stewart. 



A. 43. Two half-grown specimens of a Sun-star (Solaster pap- 

 posus). The viscera and upper (abactinal) body-walls have 

 been removed from the lower specimen. The ambulacral 

 plates including those of the oral system, the plates in the 

 interradial septa (interbrachial pillars), and the stone-canal 

 constitute the endoskeleton. From the upper specimen 

 have been removed the whole of the body-walls excepting 

 the adambulacral plates. Presented by Prof. C. Stewart. 



A. 44. A Snake-armed Starfish (Ophiocoma erinaceus). The 

 viscera and upper (abactinal) wall of the disc have been 

 removed to show the ossicles about the mouth, and the 

 vertebral ossicles ( = fused ambulacral plates) that are con- 

 tinued from the arms into the disc. One arm has been 

 detached with the six vertebral ossicles that were included 

 in the disc. Some of the vertebral ossicles of the arm have 

 been exposed by removing four of the dorsal (abactinal) 

 shields. Three vertebral ossicles are shown in different 

 positions, and below are enlarged models of these having 

 on one side the surfaces giving attachment to the inter- 

 vertebral muscles, painted red. A blue rod has been passed 

 on one side into the opening by which the lateral branch 

 of the radial water-vessel enters the ossicle, in the substance 

 of which it forms a loop, and emerges in a cup-like de- 

 pression to which the tube-foot is attached. The vertebral 

 ossicles and oral skeleton form the endoskeleton. 



Presented by Prof. C. Stewart. 

 Ludwig, Zeitschr. wiss. Zool., Bd. xxxi. 1878, p. 347. 



A. 45. EcHnometra lucunter. The shell (corona) has been cut 

 in half, and the spines removed. The lower half shows five 

 arch-like processes (auricula) that project into the interior 

 and give attachment to certain of the jaw-muscles. The 

 upper half shows the five genital organs (gonads) ; these, 

 together with the intestine, mesentery, and other organs, 

 are stiffened by numerous characteristic spicules that, like 



