Microscopical Essays. 



3«3 



Mr. William Andre has (hewn, that thefe are not the only 

 variations which are to be found in the eyes of thefe fmall crea- 

 tures ; for thofe of the monoculus polyphemus are made up of a 

 great number of fmall tranfparent amber-like cones. See his 

 letter to Sir Jofeph Banks, in the Philofophical TranfacHons, 

 a (hort extracl from which I (hall proceed to lay before the 

 reader., 



« The monoculus polyphemus, or king crab, is a cruftaceous 

 animal, found in all the feas furrounding the continent of America' 

 and the Weft India iflands, and which frequently grows to a very 

 large fize. 



« If the {hell of the monoculus were divided fairly in half, the: 

 large eyes would be nearly in the center of each piece, and the 

 fmall ones on the divided edge, near the fore-part of the {hell . 

 The large eyes are at a great diftance from each other ; but the* 

 fmall ones are clofe together. It will appear hereafter that the 

 large eyes are made up of a great number of fmall tranfparent 

 amber-like cones, and that the fmall ones are compofed of one 

 fuch cone only : fo that they may be divided into eyes with many 

 cones, and eyes with a fmgle cone. The large eyes,, or thofe 

 with many cones, appear as two tranfparent fpots, about the fize 

 and nearly of the fhape ef a kidney-bean, the concave edges 

 looking towards each other, and the convex towards the edge of 

 the fhell. If they be examined attentively, we may difcern on 

 their furface a number of fmall depreffions, which point out the 

 center of each cone. The fmall eyes, or thofe with a fmgle cone,, 

 look like two fmall tranfparent fpots, not larger than a pin's 

 head ; thefe, from their minutenefs, are eafily overlooked. 



" The. 



