MARINE BIOLOGICAL STATION AT PORT ERIN. 25 



from F 11 to F 16, and the exposures varied from 10 to 

 15 seconds. 



" For this kind of work the best lens is one of about 

 •3-inch focal length, the magnification being obtained by 

 having the plate a considerable length from the lens ; by 

 this means the whole thickness of the object to be photo- 

 graphed can be brought into focus without having to use 

 a small stop and so sacrifice light. 



" These photographs were taken with the cell in a 

 vertical position, and the cell used was just the depth of 

 the object to be photographed, which object was kept in 

 position by the cover glass. This method entails 

 considerable trouble, and there is a danger that the 

 specimen may be compressed. 



,( Since returning from Port Erin I have constructed a 

 more elaborate apparatus, so as to be able on my next 

 visit to photograph specimens with the cell in a horizontal 

 position, and so avoid all risk of compression. 



"I have to thank Mr. Chadwick, and his assistant, 

 Mr. T. Cregeen, for the immense trouble they took in 

 procuring suitable specimens in the successive stages, and 

 Mr. W. J. Dakin for many useful suggestions." 



In addition to the above described work by Dr. F. 

 Ward, our Eon. Treas., Mr. Edwin Thompson, has devoted 

 much attention during the year to making Photomicro- 

 graphs of living Plankton. Fig. 5 shows four oi his series 

 illustrating the embryonic development of the plaice. 

 These all represent earlier stages than those figured by 

 Dr. Ward (PI. II.), which commenced with the hatching 

 of the LarvsB. Mr, Thompson has also prepared a oumber 

 of photomicrographs of typical samples of different kinds 

 of plankton, and a lew of these are Bhown in PL [., p.:;;}. 



