APPENDIX. 13) 
same species. It is perfectly free, and so simple in 
its structure, that when the sac which forms its body 
is turned inside out it will continue to perform the 
functions of life as before. The greater part, however, 
of these Hydraform Polypes, although equally simple 
as individuals, are connected in a compound life by 
means of their variously formed polypidom, as the 
branched system of cells is termed. The Hydroid 
Zoophytes are represented in the first plate by the 
following examples. 
HYDROIDA. 
SERTULARIA ROSEA. Jl. I. jig. 6. 
A species which has the cells in pairs on opposite 
sides of the central tube, with the openings turned 
outwards. In the more enlarged figure is seen a 
septum across the inner part of each cell which 
forms the base upon which the polype rests. Jig. 
6 6 indicates the natural size of the piece of branch 
represented; but it must be remembered that this 
is only & smail portion of the bushy shrub. 
