<w a Craspedote Flagellate Infusoria n. 73 



scribe this sponge as if it were to be the type for future com- 

 parison. 



General plan. — The whole individual sponge is endowed 

 with a double envelope (PI. XI. fig. l,aa', cd) the outer and 

 inner parts of which are directly continuous with 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, Avhere they rest on the broAvn mass of monads. In brief, 

 we might say that the sponge is covered with a miniature co- 

 lonnade, 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 be- 

 neath. These are the afferent ostioles (os), through and into 

 which a constant current of floating particles may be seen 

 moving Avith considerable vivacity. Here and there, scattered 

 at wide distances, flngcr-like hollow processes from the outer 

 division arise singly and at various angles. Each is termi- 

 nated 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 Avhen fully extended, and of the 

 proportions and taper of the human fore finger. 



Plunging the focus of the objective to the floor of tlie co- 

 lonnade, the inner division (c) there is found to be pierced by 

 much more numerous openings (<), but far smaller in diameter 

 and quite methodically arranged, each one corresponding to 

 and overlying a hollow group of monads {h). The outer divi- 

 sion is further embellished with irregularly scattered minute 

 spicules (e'), which lie imbedded in the cytoblastema, parallel 

 with the surfiice of the envelope, and occasionally crossing 



