WORMS. 9 



does not occur. In the months of July and August pairing 

 takes place, when each worm fertilizes the eggs of the 

 other. 



Along the middle of the back a row of pores may be 

 detected by close examination, one in each segment, with 

 some few exceptions, which lead into the body cavity. 



In the earthworm there are no specialized breathing- 

 organs, but aeration of the blood is effected through the 

 whole skin. The sense-organs are also wanting, though 

 the animal is susceptible to light-impressions, as may be 

 easily proved. A few worms may be kept in a pot of 

 damp earth, and when the room is dark they will come to 

 the surface: bullet direct rays of light fall upon them, and 

 they will hastily retreat. According to Hofffneistcr. these 

 light-impressions are only received by the first two rings. 



If a cross section of the body of the worm is made by 

 the teacher, the relative position of the internal organs 

 may be seen. Fig. 2 represents such a section. 



Beneath the thin, outer cuticle (Fig. 2. 0) there lies 

 a thicker, transparent, and cellular layer known as the 

 hypodermis (hy). Internal to this layer are bands of 

 circular muscles, which extend continuously around 

 the body of the worm (</ 1). These bands are under- 

 laid by five thicker bands of longitudinal muscles, which 

 run the length of the body (</ 2). Muscular septa 

 extend inwards to the intestine, dividing the body 

 cavity into separate chambers for every segment, ex- 

 cept a few in the anterior part (// 3). 



s is one of the eight setai which are developed in 

 sacs, and pass outward. Above the intestine (r) lies 

 the pseudhaemal vessel already described (//»), and 

 below it the nerve cord (f/s) , which runs along the 

 floor of the body. 



