132 MARINE INVERTEBRATES 
long, which is divided into a number of concentric, communicating com- 
partments. The margin of the float is entire, and a triangular sail 
extends diagonally across the top. On the under side is a single mouth 
on a manubrium, and surrounding it are a large number of short thread- 
like appendages having different functions. Some of them are feelers, 
others bear reproductive buds, and others have stinging-cells. Associ- 
ated with Vellelais an allied hydroid called Porpita, which has no sail, 
and in company with these two is a jellyfish called Rataria, which is 
supposed to be the offspring of one or the other of them. 
