ORGANIC EVOLUTION 163 



The record of the work done may consist in the following 

 figures : 



1. Positions of hydra at rest, and form of body extended 

 and contracted. 



2. Buds in various stages of development. 



3. Sexual organs, if found, and the sex cells if these can 

 be made out. 



4. Nematocysts in the tentacle, and the same discharged." 



5. Cross section of the body, drawn from section. 



6. Diagram of a longitudinal section of body. 



THE EARTHWORM.* 



To every one who turns the soil in flower bed or garden 

 this animal is very familiar. It assists in tillage by perforat- 

 ing the soil with its burrows, and by carrying subsoil up 

 from below in the "castings" which it strews around the 

 mouth of its burrow, and mixes with the humus. Being 

 nocturnal and blind, its activities may be easily observed 

 with a lantern on a wet night, when it will be found partly 

 extended from its burrow, reaching about over the soil from 

 its doorway, ever ready to make a quick retreat if disturbed. 

 If seized quickly and held for a moment until it releases its 

 hold on the walls of its burrow, it may then be pulled out of 

 it; this is the way to get specimens for study. 



External features. The body of the worm is segmented : 

 i. e., it consists of a series of transverse rings or segments 

 (somites'). There is no head and no tail, but there are 

 definite front and hind ends. At the former is the mouth, 

 overhung by a muscular flap or fold, the prostomium, 

 which, in absence of arms or tentacles, assists in getting food 

 into the mouth ; at the other end is the anus ; and the ali- 

 mentary canal extends straight through the middle of the 

 body from end to end. 



*The following outlines apply especially to the large Lumbricus 

 herculeus,v?hich, on account of its size, is a favorable form for dis- 

 section. 



