341 



EXPLANATION OF THE FKJUHES ' 



SINCE I have prepared tin- figures for tin- most part without the ail 

 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 1 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. 1 >ears witness, for example. Since the size of tin- 

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

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

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

 with Zeiss's Apochr. 2 mm., Ap. 1 - 30 or T40, and the Comp. Oculars 

 12 or 18. 



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

 obtained from Professor Butschli, /oologisches Institut, Hc-idellu-rg, by si/nd- 

 ing the sum of live shillings. 



