46 H. M. BERNARD. 



EXPLANATION OF PLATE 3, 



Illustrating Mr. H. M. Bernard's " Studies in the Retina : 

 Rods and Cones in tlie Frog and in some other 

 Amphibia." 



Frog. — Fig. 1. — The cones of the frog as usually seen, with true tips 

 broken off. The asterisk marks the junctions of inner and outer limbs, where 

 the elements often further divide under the action of reagents. 



Fig. 2. — Selection of elements from the retina of the adult frog which have 

 been measured, and arranged on a scale graduated in sections of 10 /u. 



Fig. 3. — Further selection from the same, the parts not measured. 



Fig. 4. — A series of elements arranged according to the lengths of the parts, 

 • showing how the cones may be developmental series in the formation of new 

 rods. 



Fig. 5. — A selection of " double cones " from the retina of the frog ; a alone 

 has the tips preserved (see text). 



Toad. — Fig. 6. — A selection of elements from the retina of the adult toad. 

 The large size of the ellipsoid is shown ; c? is a double cone ; h is also a 

 double cone without basal vacuole in the younger of the two, i. e. in the one 

 on the left. 



Fig. 7. — Selection of same arranged on a scale corresponding with Fig. 4 of 

 the frog. 



Axolotl. — Fig. 8. — Series of elements from retina of adult axolotl, to 

 show how the cones pass into rods ; c shows a " double cone." 



Salamander. — Fig. 9. — A few elements from the retina of the sala- 

 mander. 



Fig. 10. — A cone between two rods of an adult salamander. The cone has 

 what appears to be a terminal vesicle (cf. Fig. 2, a, d,f,g, and Fig. 9, a and b). 



Fig. 11. — A few elements from retina of young salamander (eye diameter 

 1'6 mm.), showing three cones at different stages of development, forcing 

 their way down between two rods. The rest of space was probably occupied 

 by one or more of the earlier sac-like elements. Cf. Fig. 16. 



Toad, Young. — Fig. 12. — a and b. Elements from near the centre of 

 the retina of a toad tadpole, c. Slightly nearer the periphery, b. Shows the 



