108 The American Sjpongilla. 



the inner division (c) there is found to be pierced by much more 

 numerous openings (i), but far smaller in diameter, and quite 

 methodically arranged, each one corresponding to and overlying a 

 hollow group of monads {h). The outer division is further 

 embellished with irregularly-scattered minute spicules (e^), which 

 lie imbedded in the cytoblastema, parallel with the surface of the 

 envelope, and occasionally crossing each other at various angles. 

 To complete this general sketch, we will state more definitely the 

 relation of the constituents of the monadigerous mass. There 

 are essentially but two elements here ; namely, the inner division (c) 

 of the investing membrane, and the groups of monads (A) which 

 are imbedded into it, below its surface. In a fully-expanded 

 individual these groups seldom lie so closely as to touch each other. 

 They vary considerably in size and are usually globular or 

 spheroidal, and form a single stratum, with rather narrow inter- 

 spaces (c') between them. 



It seems proper here, at least for the sake of precision, that the 

 cytoUastematous basis, in which the monad groups are imbedded, 

 should be considered apart from the epithelium-like, inner (c) in- 

 vesting membrane which overlies it, although the two are essen- 

 tially one ; the epithelioid membrane, by prolonging itself between 

 (at c^) and beneath the groups, forming for them a continuous 

 foundation. In this light, then, we shall speak of the monadige- 

 rous mass as consisting of three elements, namely, the inner invest- 

 ing membrane proper, the group of monads, and the cytoblastematous 

 basis. This basis seems to constitute a large part of the bulk of 

 the body, since it occupies all of the interior space beneath the 

 monad groups. In specimens which grow over flat surfaces in de- 

 pressed patches, or around stems of plants, it forms a relatively 

 thin layer ; but where the body stands out an irregularly-rounded 

 mass, sometimes an inch in diameter, the cytoblastematous basis 

 fills up the interior, in enormous proportion to the bulk of the 

 monad layer. 



Obganography. 



TJie Investing Membrane. — The investing: membrane (Fig. 1, a, 

 a}, c, d) consists essentially of two histological elements, namely, 

 a very diffuse cytoblastema (a^) and irregularly - disposed cells 

 (b, b\ b') scattered through it. The intercellular cytoblastema 

 forms a very thin layer (a') between the cells (b) ; but where the 

 latter are imbedded in it, its outer and inner faces are as wide apart 

 as the considerable depth of the cells demands ; and thus it happens 

 that the membrane (both the outer and the inner divisions) pre- 

 sents in profile (a\ c, d) such an irregular thickness. The cyto- 

 blastema (a)) is colourless, hyaline, and ajiparently homogeneous 

 under a low power; but when magnified to about four hundred 



