250 EVENINGS AT THE MICROSCOPE 



appreciable breadth or thickness, being scarcely more than 

 the extended line formed by the successive points of 

 origin of the limbs. 



The head, however, is distinct and well furnished. It 

 is crowned with a short column, much as in the Harvest- 

 man, on the summit of which are placed four black eyes, 

 set in square; these, under the magnifying power which 

 we are applying to them, gleam like diamonds, the light 

 being highly refracted through them. It is the high re- 

 fractive power of these eyes, as of those which we have 

 lately been examining, which makes them appear black; 

 for, as I have explained, they are really transparent lenses, 

 covered with polished corneas, and furnished with the 

 other essentials requisite for the transmission of the rays 

 of light to the optic nerve, or, as in this case, direct to 

 the brain. 



In front, you see the head projects into a stout oval 

 or cylindrical proboscis, terminating in a small mouth and 

 stout jaws, and furnished at the sides with a pair of spine- 

 like palpi, and a pair of pincer-claws (modified antennae) 

 somewhat resembling the nippers of a Crab or Lobster. 



Such is the outward form of this tiny speck, the whole 

 body of which scarcely equals in dimensions a quarter of 

 an inch of sewing cotton. And now I will beg your atten- 

 tion to the singular manner in which digestion is carried 

 on in this atom, which you will discern plainly enough 

 through its brown but translucent skin. If you look care- 

 fully at either of the long, many- jointed legs, you will see 

 that it is permeated by a central vessel, the walls of which 

 contract periodically with a pulsation closely resembling 

 that of a heart, by which granules or pellucid corpuscles, 

 floating in a clear fluid, are forced forward. There is no 



