The American Spongilla. 107 



in our endeavours with the minuter individuals, which occasionally, 

 we found, would allow a view through and through their entire 

 bulk, and of course left full opportunity for a satisfactory study of 

 the details of special parts, without our resorting to the dissecting 

 needles. Anyone who knows, hy experience, the intense contrac- 

 tility of the living sponge, can appreciate the advantage of not 

 being obliged to destroy and sever parts of an organism from their 

 natural relations. Premising thus, that everything has been 

 studied in " place," even to the details of the monads, we shall 

 endeavour to describe this sponge as if it were to be the type for 

 future comparison. 



General Flan. — The whole individual sponge is endowed with 

 a double envelope (Fig. 1, a, a}, c, d), the outer and inner parts of 

 which are directly continuous into each other at many points. 

 The outer division {a, a^) lies at a considerable distance from the 

 monadigerous mass {g), and is, as it were, suspended on the points of 

 the larger, far-projecting spicules (e) ; just as a tent canvas is 

 supported on the ends of poles. The inner division (c) closely 

 embraces the monadigerous mass like an epidermis, and even 

 plunges between the hollow groups of monads, forming to them a 

 basis of support. The outer and inner divisions are continuous 

 with each other at many points, as stated just now, but only where 

 the larger spicules project. There the envelope [d) runs along 

 the spicules, completely embracing them, as if in a sheath, from 

 their tips to their bases, where they rest on the brown mass of 

 monads. In brief, we might say that the sponge is covered with 

 a miniature colonnade, whose ceiling is the outer division of the 

 envelope, the pillars are the bundles of spicules, and the floor is 

 tapestried by the inner division, which about the pillars hangs from 

 the ceiling in lofty folds. The continuity of the outer division of 

 the envelope is broken by numerous round or oval openings, of 

 various and frequently changing sizes, sometimes very large, 

 which allow a free ingress of the water to the space just beneath. 

 These are the afferent osHoles (os), through and into which a 

 constant current of floating particles may be seen moving with 

 considerable vivacity. Here and there, scattered at wide distances, 

 finger-like, hollow processes from the outer division arise singly 

 and at various angles. Each is terminated by a large aperture, 

 the efferent ostiole, from which a current of water and floating 

 matter emerges with more or less spasmodic irregularity. The 

 smaller individuals, from half a line to half an inch in diameter, 

 possess only one such ostiole ; and those an inch in diameter 

 seldom have more than two or three like conduits ; but they are 

 very large, sometimes a quarter of an inch in length when fully 

 extended, and of the proportions and taper of the human forefinger. 

 Plunging the focus of the objective to the floor of the colonnade. 



