STAEriSH 107 



Extend the cut along the sides of each ray to the disk, 

 in such a manner as to free the roof of the rays and disk 

 from the lower part. Be careful not to injure the in- 

 ternal organs with the tips of the scissors. Bend back 

 the cut portions and notice : 



or. The body-cavity, coelom, or peri- visceral cavity. 



— What is its shape ? How is it formed ? What 

 does it contain ? Is it single or divided into com- 

 partments ? Note the smooth, glistening mem- 

 brane lining the cavity. Examine microscopically 

 a drop of fluid from the body-cavity of a living 

 starfish. 



A. — The Digestive /System. 

 a. The hepatic cceca or "liver" (physiologicallj'^, a 

 pancreas). — How many in each ray ? Do they 

 entirely fill the ray ? How are they arranged ? 

 To what are they attached ? How held in place ? 

 What is their color ? Structure ? With what do 

 they communicate ? By what means ? 



Attaching the hepatic coeca to the roof of the 

 ray is 



i. The mesentery. — What is its position ? How many 

 in each ray? Texture? Color? ISTotice that the 

 mesentery is continuous with the membrane 

 which lines the body-cavity. Try to prove that 

 the membrane consists of a double fold. 



c. The stomach. — What part of the body-cavity does 

 it occupy ? Note that it is divided into a pouched 

 or cardiac portion and a pentagonal or pyloric 

 portion. Study the arrangement, shape, size, and 

 structure of the pouches. Examine the mem- 



