252 EVENINGS AT THE MICROSCOPE, 



for the transmission of the rajs 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 

 vrhole body of which scarcely equals in dimensions a 

 quarter of an inch of sewing cotton. And now I will 

 beg your attention to the singular manner in which di- 

 gestion is carried on in this atom, which you will dis- 

 cern plainly enough through its brown but translucent 

 skin. If you look carefully at either of the long, many- 

 jointed legs, you will see that it is permeated by a cen- 

 tral vessel, the walls of which contract periodically 

 M'ith a pulsation closely resembling that of a heart, by 

 which granules or j^ellucid corpuscles, floating in a cleai 

 fluid, are forced forward. There is no uniformity in 

 the direction of the pulsatory waves ; sometimes, as in 

 the limb we are watching, they proceed from the body 

 towards the extremity ; but, in some of the others, Ave 

 shall probably find, even at the same moment, that the 

 waves have a retrograde course ; and this contrariety 

 may occur in two contiguous limbs on the same side 

 of the animal. By continuing our observation for 

 some minutes, we shall find also that its force is varv- 

 ing and uncertain ; strong and regular at one time, weak 

 and vacillating at another, and sometimes even quite 

 intermitted, or at least, quite imperceptible. 



By selecting a limb in which the movements are 

 strong, you may trace the vessel to its termination in a 



