92 THE BIOLOGY OF THE ANIMAL 



ferences among the buds or zooids occupying 

 the branches ? How many kinds are distinguish- 

 able? Is the transparent covering or perisarc 

 continuous over the entire cluster ? Is the fleshy 

 part or ccenosarc continuous? 



5. The perisarc. — Of what does it appear to be com- 

 posed? What is its color? Does it vary in 

 thickness in different parts of the cluster? Ex- 

 plain. Note the annulations at the bases of the 

 branches. Do these annulations occur anywhere 

 else? What is the usual number of annulations 

 on a branch ? 



c. The ccenosarc. — Where is it most plainly seen ? Is 



it attached to the perisarc at all points ? Is it 

 everywhere covered by the perisarc ? Note that 

 it is composed of two distinct layers of cells, the 

 ectoderm or outside layer, and the entoderm or 

 inside layer. How do these compare in thick- 

 ness ? In color ? How are they connected ? Do 

 you notice any differences between the cells com- 

 posing each layer? Can you detect a third or 

 supporting layer lying between the other two ? 

 How do you distinguish it from them? Are 

 these layers traceable everywhere in the cceno- 

 sarc? Compare with Hydra. Notice that 

 through the centre of the ccenosarc runs a 

 tube or body-cavity. Can you trace this tube 

 throughout the entire colony ? 



d. The zooids. — Endeavor to find the kinds men- 



tioned below : 

 1. The feeding zooids or hydranths. — What is their 

 position in the cluster? Their shape? Are 



