ANNULATA. 199 



Circulation and Its Organs. Can you see the dorsal blood vessel 

 through the body wall in the living specimen? Look at several. 

 Is there any trace of pulsations? Compress the worm slightly and 

 see if you can discover any other vessels. There is a ventral vessel 

 which may be seen under favorable condition. There are also 

 several circular vessels (hearts) looping the digestive tube and con- 

 necting the dorsal and ventral vessels (Fig. 56, c.v). In what 

 direction does the blood flow in the main vessels? There are numer- 

 ous other smaller vessels, with capillaries in the body wall, in the 

 walls of the digestive tract, and of the excretory tubules. What 

 are the functions of each of these sets of capillaries? 



Excretion and the Excretory Organs. In Fig. 13 is seen a diagram 

 of an excretory tubule of a worm. How many of these in the earth- 

 worm? How are they arranged? How are they supposed to do 

 their work? 



Reproduction and Development. The earthworm contains both 

 sets of sexual organs in one individual. They are too complex 

 for the elementary student to work out by dissection. While an 

 individual produces both eggs and sperm there are special devices 

 to insure that the eggs will never be fertilized by the sperm from 

 the same individual. The eggs, together with sperm from another 

 individual, are deposited in a cocoon or capsule which is secreted 

 by the glands of the girdle. Within this capsule the eggs hatch and 

 the early development takes place. They do not all develop, how- 

 ever; some get the start and live upon the others, Make a separate 

 outline drawing of each set of organs in the earthworm and compare 

 it with the corresponding structures in the crayfish. Make a 

 diagram of an imaginary sagittal (i. e., median longitudinal, dorso- 

 ventral) section, showing all the structures that should show in such 

 a section. 



215. It will be seen from the preceding studies that 

 the earthworm has specialized organs for each of the 

 great animal functions except those of locomotion and 

 respiration. The body wall itself takes care of both of 

 these functions. The setae are used in locomotion, but 

 can hardly be called organs of locomotion. 



216. The Minute Fresh -water Worms. There are a 

 large number of small types of worms similar to the 

 earthworm, but on the whole more simple in their struc- 



