Branch Echinodermata 43 



middle of the body ? Can you see that these ambulacral 

 suckers are arranged in five broad bands ? 



IV. — Cut the body wall longitudinally on one side to lay 

 open the central cavity. See the long much-coiled ali- 

 mentary canal. Notice the structure of this canal; next 

 the mouth is an oesophagus ; below this is a well-defined 

 stomach; next comes the long, convoluted intestine, 

 which is small in size throughout until it opens into 

 the larger cloaca, at the posterior end. Make a sketch 

 of the alimentary canal, labelling each part. 



V. — Remove the intestine, leaving the other parts of the 



canal intact. The most noticeable objects now visible 

 are the genital gland, the respiratory tree, and, the five 

 sets of longitudinal muscles. 



VI. — The genital gland is near the middle of the upper half 

 of the body cavity. It looks like a sort of brush, being 

 composed of many slender filaments lying side by side. 

 Notice that the duct leading from these extends to an 

 opening between two of the tentacles. (The genital 

 gland may be the ovary or the testes, as the sexes are 

 separate.) 



VII. — Trace out the two main divisions of the respiratory 

 tree with their many branches. Notice the connection 

 of each half with the cloaca. In this way fresh sea 

 water reaches them. 



VIII. — Study the five sets of longitudinal muscles, extend- 

 ing up and down the body walls. Trace these out 

 carefully and describe them. Notice also the circular 

 fibres which strengthen the body wall. 



