SPIDEBS AND MITES. 219 



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

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

 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 at- 

 tention to the singular manner in which digestion is carried 

 on in this atom. You will discern it plainly enough 

 through the 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 central vessel, the walls of 

 which contract periodically with a pulsation closely resem- 

 bling that of a heart, by which granules or pellucid cor- 

 puscles, floating in a clear 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, we shall probably find, even at the 

 same moment, that the waves have an opposite course ; 

 and this contrariety may occur in two contiguous limbs on 

 the same side of the animal. By continuing our obser- 

 vation for some minutes, we shall find also that its force 

 is varying and uncertain ; strong and regular at one time, 

 weak and irregular 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 blind sac 

 in the last joint but one of the limb ; and then follow it 

 up to its junction with a great vessel which runs longi- 

 tudinally through the trunk, of which all the vessels that 

 permeate the limbs are branches, and whence the circu- 

 lating globules all proceed. This .great vessel is the 

 stomach; and this circulation is the provision for dis- 

 persing the nutritive properties of the food to all parts 

 of the system. There is in these humble and simply- 

 organised animals no proper blood, or, at least, none 



