104 HOURS WITH NATURE. 



and a lower surface. Further, all the animals of this 

 series are characterised by the possession of a true 

 body cavity, through which the alimentary canal runs, 

 somewhat, as a Zoologist of repute has graphically des- 

 cribed, like a lamp-chimney through a lamp globe. Be- 

 sides the alimentary canal, the organs of circulation, 

 excretion, and reproduction are also lodged in this 

 cavity. 



" We have no time however to study in detail all the 

 various types of animals of this series ; suffice it to say 

 that their number is very large and that their forms are 

 various with an immense diversity of gradations from 

 worm to man. 



"Lower type of worms. Do you see those tape-worms 

 there ? They are the most degraded animals of this series. 

 Degraded, because they are incapable of leading an in- 

 dependent existence, living commonly as parasites in the 

 alimentary canal of warm-blooded vertebrate animals : 

 they are also structurally incomplete, the alimentary canal 

 being almost wanting or imperfect. Each of them has a 

 wonderful story to tell you about the complicated series 

 of changes it went through in the course of its develop- 

 ment from the egg to its present mature form. The egg 

 after having escaped from the sexually mature segments 

 of the parent tape-worm found its way into the stomach 

 of some warm-blooded vertebrate animal, say a cow. 

 Here it did not at once, develop into a tape- worm complete 

 in structure like one of those in that case before you, but 



