July 7, 1910] 



NATURE 



The advantages of such an apparatus at a biological 

 station or on a research boat are obvious, for 

 specimens taken from the trawl or tow-net can be 

 placed in suitable tanks or cells by the biologist, and 



photographed, living, anaesthetised, or dead, by an 

 assistant. Any number of useful records could thus be 

 made from fresh specimens of any particular catch. 

 For photographic purposes it is desirable to obtain 

 perfect living specimens; but the photography of 



tage be employed when counting specimens in the 

 analysis of a plankton catch, for the area under the 

 field of the microscope can be thrown on to a sheet 

 of paper and the specimens ticked off. 



When working with artificial light, the 

 illuminant should be of sufficient power 

 to ensure against the want of light 

 being a hindering factor. I use a very 

 useful little arc lamp made by Messrs. 

 Leitz, when electric power is available; 

 failing this, an o.\yhydrogen light, though 

 good results can be obtained with an 

 acetylene lamp. When using arc or lime- 

 light it is necessary to have a cooling tank 

 between the light and the specimen. 



With either arc or limelight, working 

 with a Zeiss microplanar lens at F. 4'5 on 

 a medium rapid plate, a full exposure can 

 be obtained in one-tenth of a second up 

 to twenty-five magnifications. 



Reference has been made already to 

 photographs taken in natural environ- 

 ments. As an illustration of the record- 

 ing of the habits of marine animals is 

 shown the photograph of the common 

 dog-whelk (Buccinum) holding with its 

 foot the abdomen of a dead crayfish. On 

 ren^oving the crayfish it was found that 

 the whelk had partially sawn through the 

 shell by means of its radula. 



.\ characteristic movement is shown in 

 the photograph of a pecten turning itself over. 



Recently I had the opportunity of taking numerous 

 pecten photographs under the direction of Mr. W. J. 

 Dakin, and by his kind permission I am able to show 

 an instantaneous photograph of this mollusc, in the 



itf^: 







"7//£^Z'-^- 



Fig. 4. — Plaic: Larv: 



numerous imperfect specimens is also very valuable, 

 for at any time a perfect drawing can be made from 

 the material so collected. 

 As an additional use, this apparatus can with advan- 

 NO. 2123, VOL. 84] 



act of turning itself over, after having been placed 

 on the left valve. The other photographs taken 

 showed the gradual opening of the pecten, until the 

 valves werg separated as much again as in the photo- 



