EXPLANATION OF PLATES 



All the figures given on plates have been drawn at the heiglit of the object 

 stage, by Abbe's apparatus, under the same magnifying power : Zeiss' apochromat 

 homogene ipimersion 3 mm., compensations okular. 12, tube length 160 mm. 



The various figures have all been drawn from the preparations fixed by Levi's 

 solution and stained by Heidenhain's iron-alum-haematoxylin, with only the 

 exception of figure 7, which has been reproduced from the preparations by Alt- 

 mann's method, after changing the color. 



571 



