184 THE MICROSCOPE. 



two inches in thickness. From the other sponges it is distinguished 

 by the smooth spicula which surround its seed-like bodies, and the 

 matted structure. 



Spongilla alba. Its texture is coarse and open; structure reti- 

 culated. The investing membrane abounds in minute spicula; has 

 seed-like spheroidal bodies about l-30th of an inch in diameter, with 

 rough points externally. The large spicula are slightly curved, smooth 

 pointed at each end, about l-54th of an inch in length; the small 

 spicula are slightly curved, thickly spiniferous, or pointed at both ends; 

 the former, pertaining to the seed-like bodies, are about l-200th of an 

 inch in length ; the latter, pertaining to the investing membrane, are 

 more slender, and a little less in length; these last numerous small 

 spiniferous spicula when dry present a white lacey appearance, from 

 which Mr. Carter gives them the name of alba. 



SpongiUa meyeni is massive, having large lobes, mammillary emi- 

 nences, or pyramidal, compressed, obtuse or sharp-pointed projections, 

 of an inch or more in height; also low wavy ridges. Its seed-like 

 bodies are spheroidal, about l-47th of an inch in diameter, studded 

 with little toothed disks. 



Spongilla plumosa. This is much the same in appearance and 

 colour as the last, but looser and coarser in its texture and structure. 



Mr. Carter states : " That fresh-water sponge is composed of a fleshy 

 mass, supported on a fibrous, reticulated, horny skeleton. The fleshy 

 mass contains a great number of seed-like bodies in all stages of deve- 

 lopment, and the horny skeleton is permeated throughout with siliceous 

 spicula. When the fleshy mass is examined by the aid of a micro- 

 scope, it is found to be .composed of a number of cells, imbedded in and 

 held together by an intercellular substance. 



The granules are round or oval ; translucent, and of an emerald 

 or yellowish-green colour, varying in diameter below the 12,000th part 

 of an inch, which is the average linear measurement of the largest. In 

 some cells they are so minute and colourless as to appear only under 

 the form of a .nebular mass ; while in others they .are of the largest 

 kind, and few in number. 



The hyaline vesicles, on the other hand, are transparent, colourless, 

 and globular; and although variable in point of size, like the green 

 granules, are seldom recognised before they much exceed the latter in 

 diameter. They generally possess the remarkable property of slowly 

 dilating and contracting themselves, and present in their interior mole- 

 cules of extreme minuteness in rapid commotion. 



The intercellular substance, which forms the bond of union between 



