84 EYE OF DYTISCUS 



The eye of Dytiscus marginalis is always 

 considered a beautiful object for the micro- 

 scope. The face of a watch and portraits of 

 the late Queen have frequently been photo- 

 graphed through the facets or ocelli of this 

 beetle's eye. A small portion of the eye is 

 best for this purpose, because it is easier to 

 flatten out a tiny area than the whole cup- 

 shaped exterior. 



Glaus sums up particulars of the creature 

 in the following words : ' Swimming-beetles, 

 with filiform ten- or eleven- jointed antennae 

 and broad swimming-legs beset with setae ; 

 the hind legs project back and are especially 

 adapted for swimming by the possession of a 

 close covering of swimming hairs. 7 



The illustration (Fig. 20) is taken from a 

 photo-micrograph of 550 diameters; the time 

 of exposure was 10 minutes; the focal length 

 was 20 inches; the objective was the ^th, 

 and an eye-piece of 5 diameters was used. 



The illustration (Fig. 21) is from a negative 

 of 32 diameters. 



