ANTHOZOA HYDROIDA. 83 



general fleshy substance of the body. The growth of the 

 polypidom is dependent on the growth of the pulp, or rather 

 they grow together, as the feathers, beak, and claws increase 

 in size on a young growing bird. 



Careful observations have been made on the polypidom, 

 with its included pulpy matter, and the result is as follows. 

 The ovule, when matured, drops from the vesicle, and fixes 

 on some rock, or seaweed, or shell, or sometimes even on 

 some other marine animal, such as an Ascidia. Minute 

 fibres, proceeding from its under side, cause it to adhere, 

 while from the upper side the commencement of the stem 

 springs up. The structure of this shoot is at first homo- 

 geneous : gradually, however, the pulp is formed in the 

 inner part, and the shoot, having assumed a bulbous form at 

 the summit, condenses and expands, and so does the horny 

 covering, till one or more closed cells are formed. By and 

 by, little knobs protrude from the cells, and increase till 

 they become tentacula, when the cell opens and the ani- 

 mal begins to catch its prey; and from that moment it 

 is as large as ever it is at any subsequent period. But 

 though the polypes increase not in size, they increase in 

 number ; for, as the newly-formed one is constantly obtain- 

 ing nourishment, the central pulp increases and shoots 



