Organs of Invertebrate Animals. 49 



lens. It is that of an eye from which it may be supposed 

 that the lens and humours would have escaped if the open- 

 ing in the cornea had been a little larger. It is a case in 

 which, if the lens and humours had escaped in this manner, 

 it is not difficult to detect a sort of likeness between the 

 open and empty eyeball and the sucker on the arm, or 

 even between it and an actual polype, for the ciliary 

 processes may be supposed to repeat the radiating 

 ridges around the throat of the sucker, and the crown of 

 tentacles around the mouth of the polype. After what 

 has been said, all this may be conceded as not im- 

 probable : and if so, then the particular construction of 

 the eye becomes in some measure intelligible, and at the 

 same time some light is thrown upon the disposition to 

 radiation and ramification which is displayed con- 

 spicuously in so very many of the appendicular organs 

 already noticed. 



6. Returning to the prawn the organs which have 

 next to be examined are the posterior and anterior 

 pairs of antennae which project in advance of the eyes, 

 and which seem, at first sight, to have little in common 

 with the parts already attended to. Each member of 

 the posterior pair has a lower portion and an upper 

 portion, with a joint between them, and also between 

 the lower portion and the head of the animal, and so 

 has each member of the anterior pair. The lower 

 portion of the member belonging to the posterior pair 

 is developed above into two prominences, one in 

 advance of the other, the hindermost being prolonged 

 into an immoveable flat spine, the foremost carrying, 

 over the joint which is there present, two long and one 

 shorter, many-jointed, tapering, antennae. The lower 

 portion of the member belonging to the anterior pair is 

 also developed above into two prominences, the one 



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