PROTOZOA TO WORMS 53 



The nervous system consists of a supra-oesophageal 

 ganglion with four posterior nerve-cords — one dorsal, 

 two lateral, and one (or perhaps two) ventral. There 

 were probably also remains of the old plexus, but this 

 is fast disappearing. The excretory system consists 

 of a pair of tubes discharging through the sides of the 

 body-wall, and having each a ciliated, funnel-shaped 

 opening in the perivisceral cavity. These have re- 

 ceived the name of nephridia. Through these also 

 the eggs and spermatozoa are discharged. The repro- 

 ductive organs are modified patches of the peritoneum, 

 or lining of the perivisceral cavity. 



The number of muscles or muscular layers has been 

 reduced in this animal. But such a reduction in the 

 number of like parts in any animal is a sign of prog- 

 ress. And the longitudinal muscles have increased 

 in size and strength, and the animal moves by writh- 

 ing. Such a worm has the general plan of the body of 

 the higher forms fairly well, though rudely, sketched. 

 Many improvements will come, and details be added. 

 But the rudiments of the trunk of even our own bodies 

 are already visible. Head, in any proper sense of the 

 term, and skeleton are still lacking; they remain to 

 be developed. 



And yet, taking the most hopeful view possible con- 

 cerning the animal kingdom, its prospects of attain- 

 ing anything very lofty seem at this point poor. Its 

 highest representative is a headless trunk, without 

 skeleton or legs. It has no brain in any proper sense 

 of the word, its sense-organs are feeble ; it moves by 

 writhing. Its life is devoted to digestion and repro- 

 duction. Whatever higher organs it has are subsid- 

 iary to these lower functions. And yet it has taken 



