EXPLANATION OF FIGURES. 



All the Figures, unless otherwise stated, were drawn with the aid of an Abbe 

 camera lucida, and represent the appearance of the anterior faces of the sections. 

 Plates I.-IV. were made from preparations of Rana sylvatica Le Conte ; Plates 

 V.-VIII. from Rana sylvatica Le Conte, Bufo americanus Le Conte, and Ambly- 



stoma punctatum Linn. 



