378 Mr. J. W. Hulke on the Chameleon's Retina. [June 15, 



the stem), which rapidly augments, both in absolute and in proportional 

 size, when the development of the dorsal cirri is taking place from its 

 convex surface. By the end of the Pentacrinoid stage, this plate has ex- 

 tended itself so far over the base of the calyx as completely to conceal the 

 basals ; and as the free Autedon advances towards maturity, it gradually 

 extends itself over the first radials, which then become adherent to it and to 

 each other. The basals then undergo a most curious metamorphosis, con- 

 sisting in absorption in one part and extension in another, by which they 

 finally become converted into five peculiarly shaped pieces, the ultimate 

 union of which forms the single rosette-like plate, which has been already 

 stated to lie within the annulus formed by the first radials of the adult 

 Antedon. Hence the calyx finally comes to be thus composed : 



R 3 R 3 R 3 R 3 R 3 

 R 2 R 2 R 2 R 2 R 2 



y 



CENTRO-DORSAL. 



As the orals and the anal have entirely disappeared, no part of the pri- 

 mordial calyx of the Pentacrinoid larva is traceable in it, until we separate 

 the adherent pieces which form its base, and search out the minute and 

 delicate rosette-like plate which is formed by the metamorphosis of the 

 basals. 



The structure, physiology, and development of the digestive, circulatory, 

 and respiratory apparatus, and of the nervous and muscular systems, will 

 form the subject of a future memoir. 



XVII. " On the Chameleon's Retina ; a further contribution to the 

 Minute Anatomy of the Retina of Amphibia and Reptiles." By 

 J. W. HULKE, Esq. Communicated by WILLIAM BOWMAN, 

 Esq. 



(Abstract.) 



The Chameleon's retina is peculiar in having a fovea and pecten, and in 

 the nervous conducting fibres crossing the connective-tissue fibres in- 

 stead of running parallel to them. The fovea was discovered by Knox 

 in 1823, and minutely described by H. Miiller, who also discovered 

 the singular arrangement of the two sets of fibres in 1862. It is 

 a circular pit situated at the posterior pole of the eyeball. A dark 

 brown dot, surrounded by a lighter areola, marks its centre. Here 

 the bacillary layer, which contains cones only, is alone present. The 

 cones of the fovea are long, slender cylinders placed vertically upon 

 the choroid. From the centre of the fovea outwards, the cones become 

 stouter, shorter, and more numerous towards the periphery of the retina, 



