BRYOZOA. 



115 



Beneath the first enlargement, the digestive apparatus becomes 

 narrower, but immediately expands again, and offers at this 

 point a certain number of filiform appendages, which appear to 

 be free and floating in the interior of the cell. To the second 

 cavity succeeds a narrow canal, opening into a third dilatation, 

 generally of a spherical form. From the last-named viscus 

 issues a kind of intestine, which soon bends upon itself and be- 

 comes attached to an organ of a soft and membranous texture, 

 having the appearance of a caecum, and which seems to be con- 

 tinuous superiorly with the digestive tube ; the latter continues 

 its progress towards the upper part of the cell, and ultimately ter- 

 minates by a distinct anal aperture upon the upper aspect of the 

 tentacular sheath. 



The operculum which closes the cell in Flustra and Eschara is 

 moved by two muscular fasciculi inserted into the internal face of 

 this valve by the intermedium of two filaments analogous to ten- 

 dons : by their inferior extremity, these muscles are attached to 

 the walls of the cell ; and when, by its own elasticity, the operculum 

 is turned back, and the mouth of the cell thus opened, they, by 

 their contraction, can close it like a door. 



(151.) A very singular form of Bryozoon is met with in fresh 

 water, of which the Cristatella Mucedo* is an example that has 

 undergone minute investigation. 



The Cristatella (Jig. 47, 3) consists of a common body or enve- 

 lope (d), which is Fig. 47. 

 membranous, and 

 slightly cordiform ; 

 its surface is tubercu- 

 lated,and it is incapa- 

 ble of con traction. In 

 this outer covering 

 several individuals 

 are contained, but, al- 

 though produced from 

 one another, they are 

 only aggregated, be- 

 ing lodged in distinct tubular cells. The body of each animal 

 appears to consist of a digestive canal, constricted once or twice 



* M. Turpin, Etude microscopique de la Cristatella Mucedo, espece de polype 

 d'eau douce. Ann. des Sciences Nat. for 1837. Also, another memoir upon the same 

 subject, by M. P. Gervais. Ibid. 



