58 THE EARTHWORM 



drawing the worm through the fingers from tail to 

 head. The sets are to be regarded as special loca- 

 lised thickenings of the cuticle. 



The setcB are easily isolated by boiling a bit of a worm in 

 a solution of caustic potash : they should then be washed and 

 mounted in glycerine, or dried and mounted in balsam. 



Each seta is sigmoidally curved : it is thickest at 

 its middle, and tapers towards each end. 



7. External apertures. 



a. The mouth is a small crescentic aperture on the 



ventral surface of the first segment. It is over- 

 hung by the prostomium or cephalic lobe. 



b. The anus is an oval aperture at the hinder end of 



the body. 



c. The genital apertures are four pairs. 



i. The apertures of the vasa deferentia are situated 

 on the ventral surface of the fifteenth segment, 

 one on each side, slightly to the outer side of 

 the inner double row of sets. They have 

 tumid lips. 



ii. The apertures of the oviducts are similarly 

 situated in the fourteenth segment. They are 

 minute transverse slits not seen so easily as- 

 the male apertures, their lips not being tumid. 



iii. The apertures of the spermathecse or receptaeula 

 seminis, of which there are two pairs, are 

 situated in the grooves between the segments 

 and in the line of the outer row of setae, the 

 first pair between segments ix. and x., the 

 posterior pair between segments x. and xi. 



d. The excretory apertures are difficult to see. Each 



segment, except the first three and the last, has- 

 one on each side, on the ventral surface a little 

 in front of the outer seta of the inner double row. 



To see these apertures, strip off the cuticle from the 

 anterior part of the worm, and examine the ivorm with a 



