341 



EXPLANATION OF THE EIGUEES i 



Since I have prepared the figures for the most part without the aid 

 of the camera, under the erroneous impression, as was afterwards found, 

 that by its help delicate protoplasmic structures could not be recognised 

 with certainty, I often have no sure means of determining the magni- 

 fication in cases where direct measurements were not taken. In general, 

 however, the figures relating to protoplasmic structures are drawn with 

 a magnification of about 2500 to 3500 diameters, as is proved by those 

 in which the magnification was actually determined. As I have said, 

 I convinced myself at a later period that, in preparations of sufficient 

 clearness, the protoplasmic structures can be drawn quite well by the 

 help of the camera, using Zeiss's 2 mm. and Oc. 18 ; to which fact 

 Fig. 2 on Plate X. bears witness, for example. Since the size of the 

 alveoli varies within relatively narrow limits, that is to say, between 

 0-5 to 1 /i, the magnifications can be determined fairly well from this 

 fact. Whenever it is not stated otherwise, the figures are all done 

 with Zeiss's Apochr. 2 mm., Ap. 1-30 or 1-40, and the Comp. Ocular.? 

 12 or 18. 



1 An Atlas of 19 Microphotographs in connection with this Work can be 

 obtained from Professor Biltschli, Zoologisches Institut, Heidelberg, by send- 

 ing the sum of five shillings. 



