A TUBULARIAN HYDROMEDUSAN 163 
HYDROZOA 
A TUBULARIAN HYDROMEDUSAN (Pennaria or Bougainvillea) 
These are marine animals, and among the commonest hydro- 
medusans along our coast. As is characteristic of the group to 
which they belong, they exhibit the phenomenon of alternation 
of generations. ‘T'wo generations of individuals, a sexual and 
an asexual, alternate with each other. The latter is called 
the hydroid generation; the animal in this stage is sessile and 
colonial, and produces by budding, i.e., by asexual methods, the 
sexual generation. This latter is called the medusoid genera- 
tion; in it the animal either remains attached to the hydroid 
colony (Pennaria) and is then called a sporosac, or separates 
itself (Pennaria, Bougainvillea) and becomes a free-swimming 
jelly-fish, which is called a medusa; in either case the medusoid 
produces by sexual methods embryos which attach themselves 
to fixed objects and develop into the hydroid generation. 
The hydroid stage in Pennaria.1 In this stage these animals 
form branching colonies of polyps, which are attached to the 
rocks in shallow water. The colonies are several inches in 
length, and are found in thick clusters which often cover the 
rocks over small spaces; their color is a delicate pink. 
Place a small portion of a colony in a watch-glass of water 
or alcohol, and study it under the microscope. Observe the 
main stem of the colony and its branches, also the position 
of the polyps on the branches. Note carefully the differences 
in size between the different polyps. Which is the largest 
polyp? Study the method of branching. Has the colony a 
1 Bougainvillea or any other tubularian can also be used, with slight changes 
in the directions, 
