THE COMMON COCKROACH 143 



circulatory system. Any one who brings to the exa- 

 mination of a creature such as this the popular 

 conception of what a heart is like, will certainly fail 

 to find anything which bears the remotest resemblance 

 to such conception. There is, in fact, no compact, 

 chambered, fleshy, conical body such as we are familiar 

 with in vertebrate anatomy; the "heart," so called 

 from its function, not its form, is merely an incon- 

 spicuous, elongated, soft tube, with sundry openings in 

 its sides through which blood enters it from the body 

 at large. Nor is its position such as might have been 

 anticipated ; we must look for it, not towards that 

 side of the body which faces the ground, but on that 

 which is uppermost, for it lies along the whole length 

 of the back, just beneath the skin, in the middle line. 

 Nor, again, does this rudimentary heart communicate 

 with any system of blood-vessels for conducting the 

 blood on its tour round the body ; for the blood, on 

 being expelled from the orifice at the extremity of the 

 tube, is simply passed on through the various interstices 

 between the different viscera, until it ultimately finds 

 itself back again at the place it started from. Hence 

 it is manifest that every movement of the body which 

 in any way disturbs the relative position of the internal 

 organs, will assist, to some extent, in urging the blood 

 along its course. Nor, finally, is the blood itself 

 exactly what its name might suggest. If a cockroach 

 is wounded, blood will, of course, issue from the wound, 

 but as it is only a colourless liquid, a little stretch of 

 the imagination is required to realise that it is the 

 true nutrient fluid of the body. 



By the dissection which removes the digestive tract, 

 the main part of the nervous system is laid bare. It 

 is constructed similarly to that of the earthworm, and 



