38 Invertebrate Zoology. 



madreporic plate and stone-canal are much reduced. The 

 former will be found, as a small calcareous sphere, in the for- 

 ward part of the body. It communicates with the ring-canal 

 by a slender tube (stone-canal} , lying below and parallel to 

 the genital duct. 



Make a drawing of the water-vascular system, so far as 

 you have been able to determine its course. 



Muscular System. Note five meridional bands of 

 muscles extending the entire length of the animal. Is the 

 median band above or below? How are the retractors of 

 the tentacles and of the oesophagus arranged ? What is the 

 arrangement around the cloaca ? The body- wall is tough- 

 ened by the presence of many circular muscle fibres. How 

 are they arranged? 



Make a drawing that will illustrate the muscular arrange- 

 ment of the fore and of the hind end of the body. 



The Nervous System is not easily dissected. There is 

 a circum-oral nerve-ring, from which extend five radial 

 divisions. 



