ZOOPHYTA ASCIDIOIDA. 
243 
The cell tenanted by this polype is of a tubular, an elliptical, 
oval, or hexangular figure, circumscribed by distinct walls which 
apparently separate it from those that lie in juxtaposition, and 
hinder any intercommunity. The isolation, however, I believe 
to be more apparent than real. In Vesicularia the cells are 
apart from each other, and rise from a common tube,— the zoo- 
phyte affording by this disposition of them a very favourable ob- 
ject for observing their true connection. Now Ellis states that 
while a branch of this species was in a watch-glass of sea -water, 
on the stage of the microscope, he “ could plainly distinguish 
that the internal hollow part of the whole coralline was filled 
with the substance of the parent polype, which appeared to be 
of a tender gelatinous nature ; and upon the least extension or 
contraction of the young polypes, this tender fleshy substance 
was visibly affected ; for each one was united to it by their lower 
part or tail”* I think 1 have also noticed a distinct thread of 
communication between the polypes of the Flustra ; and 
though the closeness of their proximity, and their opacity, may 
prevent the demonstration in other genera, yet a like union may 
be probably inferred, for other conclusion seems incompatible 
with the mode of increase of the polypidoms, and the regula- 
rity of their patterns. 
The polypidom, formed in some species of a congeries of 
many thousand cells, begins with one only. This original or 
seminal cell has no sooner been completed, or even in many in- 
stances previous to its perfection, than another begins to shoot 
out from a fixed point of its parietes, the bud gradually en- 
larging and developing itself until the form and size of the pri- 
mary one has been attained.'!* This process can most easily be 
apparent when it is in a state of contraction, at which time the whole filament 
also is obviously thicker than when relaxed. The filaments have a watery tran- 
sparency and smooth surface, and under the highest powers of the microscope 
present neither an appearance of cross markings nor of a linear arrangement of 
globules.” Farre in Phil. Trans- an. 1837, p. 394. 
* Essay on Corallines, p. 21. 
f Of Lcefling’s observations on Membranipora pilosa, Pallas says — “ Vidit 
propagari seu augeri, per gemmas a marginalibus seu extremis cellulis protrusas, 
in perfectas cellulas effingendas, e quibus polypus dein exseritur. Interdum 2 
proles ab eadem cellula, at non simul exseri, sicque series duplicari atque in la- 
titudinem pandi crustam vidit.” Elench. Zooph. p. 51. See also p. 34. 
