56 Anatomy of Sagartia Schilleriana [No. 1, 



spinis incequalibus, exterioribus brevioribus quam interior ibus. Animal 

 virescente album, tentaculis longis, 14-18 instructum. 

 a. Form of cells. 



The polyzoarium of this species is extremely variable, its form be- 

 ing altogether dependent upon that of the object to which it is attached. 

 It is either found incrusting stones or wood, or it grows on different 

 water-plants,beingthen variously contorted and apparently partially free. 

 According to this the cells undergo many variations, often so much so 

 that it is extremely difficult to determine the characters of the species. 



As a rule they are hexagonal, slightly elevated, about twice 

 as long than broad and posteriorly emarginated (pi. XII, fig. 1, f). 

 The base and the sides are in full grown cells always solid, the 

 upper portion more or less membranaceous, representing a usually 

 slightly convex, very thin covering. The upper margins of the solid 

 portion of the cell, — where the thin membrane is attached — are some- 

 what raised, and each cell is separated from the next by a slight furrow. 

 The aperture lies at the anterior end, being roundish and provided 

 with somewhat thickened, elevated and solid lips. The anterior portion 

 of each cell with its margin extends into the basal indendation of the 

 previous one, while the posterior margin of the aperture is much 

 more prominent, possessing a small thickened projection which is 

 posteriorly often prolonged into four, radiating spines, the outer pair of 

 these being much shorter than the inner one (see pi. XII, fig. 2). 



In consequence of the greater elevation of the posterior margin the 

 aperture, when viewed perpendicularly from above, appears almost semi- 

 circular, but viewed at about an angle of 45 degrees from the front its 

 round shape* is distinctly perceptible. The posterior upper portion of the 

 cell is always convex, thin, finely perforated, and according to the differ- 

 ent stages more or less solid. The radii or ribs originate at the upper 

 lateral solid edges and extend in a more or less regular way from 

 both sides toward the centre. Sometimes, but not usually, they unite 

 in the median line and form solid cross bars. The length of the 

 radii also varies with the age of the cells, but their number appears 

 entirely to depend upon the length of the cells, (see figs. 3, 4, pi. XII). 



* I mention this point here particularly, because the same roundish form of 

 the aperture also occurs in many marine Ccllejporce and Lepraliw, and is usually 

 stated to be semilunar, though in reality it is not so. 



