FROM THE PRAWNS EYES. 17^ 



can look at the sight I am speaking of, without 

 feeling certain that the optical process is one of 

 concave reflection and convergence of the rays ; and 

 that the reflecting surface is in the interior of the 

 globose compound eye. The reflection is seen what- 

 ever part of the eye is opposite the light, (provided it 

 be facetted of course) but is most full direct in front, 

 where no unfacetted portion can be seen. Yet it 

 certainly has no connexion ■whatever with reflection 

 from the exterior surface, as might be suggested by 

 any one who has not actually seen it : the efiect of 

 this would be a minute point of light, very difierent 

 from this broad round gleam. 



The different species of Pagurus, and Crabs, as 

 Portunus, exhibit the same phenomenon, but in a 

 lower degree ; the disk of lightbeing smaller and of less 

 brilliance ; though their eyes are larger. I have seen 

 the same appearance in the eyes of Moths and other 

 nocturnal insects ; so that doubtless it is dependent 

 on the common structure of facetted compound eyes. 



It is pretty to see the Prawn fed. When a morsel 

 of food is dropped through the water near its head, the 

 excessively long antennae, (especially the long fila- 

 ments of the superior pair, which are carried perpen- 

 dicularly upwards) seem principally to take cognizance 

 of its presence and of its qualities. The eyes, though 

 evidently alert, are I think less trusted. As the morsel 

 comes within reach, the second feet, the principal 

 organs of prehension, are stretched out, with the two 

 fingers (pincers) widely extended ; these seize it with 

 the most easy action possible, and in a moment thrust 

 it towards the mouth. 



