A Polyzoan. 47 



A POLYZOAN 



sp.). 



AFTER a colony of this Polyzoan has remained in a solu- 

 tion of caustic potash for a little time, all fleshy matter will 

 be removed, and the skeleton may be washed in water and 

 examined with a low power of the compound microscope. 



The skeleton is somewhat hardened by a deposit of lime, 

 and is known as the ccencecium. It is made up of a multi- 

 tude of little cups, zoctcia, which are arranged in double 

 rows, back to back, each zocecium having its opening or 

 "mouth' 1 directed distally. The margin of the mouth is 

 provided with one or two spines, and on one side a deep 

 indentation or sinus will be found. This sinus is on the 

 upper surface of the double row. For convenience, the 

 side of the zocecium that is directed towards the median line 

 of each double row may be called the inner, the side 

 directly opposite (lateral), the outer, the side marked by 

 the deep sinus, the upper, and the side opposite the sinus, 

 the lower. The end of the zocecium which bears the 

 "mouth" is the distal, and is directed towards the free 

 growing point ; that directed towards the attachment of the 

 double row is the proximal. It will be noted that the 

 branching of the ccencecium is always dichotomous. 



On the outer margin of the sinus of the older zocecia, 



