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 tlie 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.-f- 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 Meinbranipora pilosa, Pallas says — " Vidit 

 propagari seu augeri, per gemmas a marginalibus seu extremis cellulis protrusas, 

 in perfectas cellulas efBngendas, e quibus polypus dein exseritur. Interdum 2 

 proles ab eadem cellula, at non simid exseri, sicque series duplicari atque in la- 

 titudinem pandi cnistam vidit." Elench. Zooph. p. 51. See also p .34. 



