known Species q/" Spongilla. 105 



EXPLANATION OF THE PLATES. 



N.B. — 1. All the figures of the statoblasts are drawn to the same scale, 

 viz. l-24th to l-1800th inch, in order that their constituent parts may 

 appear under the same magnifying-power. They, however, are to a 

 certain extent diagrammatic for the sake of clearness, inasmuch as all the 

 coats are of course in contact naturally ; the chitinous coat, which is re- 

 presented by the dark line, is not quite so thick and the spicules are not 

 quite so scanty as they are represented ; but, generally speaking, the whole 

 may be considered relatively magnified on the scale above mentioned. 



2. All the " more magnified " parts or spicules are di'awn to the scale 

 of l-12th to l-6000th inch. 



.'3. The skeleton-spicules, viz. figs. 14-18, are drawn to the scale of 

 l-12th to l-l800th inch, and the rest, viz. 19-22, on much the same scale, 

 ha\'ing been traced off" those done with Ilartnack's no. 4, prism and objec- 

 tive (No. 32, p. 69). 



4. Fig. 13,/, is only magnified three diameters. 



h. It should be remembered that all sponge-measurements, both general 

 and elementary, can only be considered approximative ; for what is fixed 

 upon as a standard at one time may be upset by the measurements of 

 another, chiefly on account of the objects appearing under different 

 degrees of development in different specimens. Still there is an average 

 largest size and shape of the spicide which can easily be recognized : but 

 this too is subject to differences; for it may be thick or thin, although 

 fully developed, while the fonner is the shortest and the latter the longest. 

 'Thus varieties are numerous ; but the gi'eat point is to give the average 

 shape and size of the fully-developed object, and to avoid as much as 

 possible the variations ; for the latter confuse, while a very slight acquain- 

 tance with sponge-structure points out that their existence may be in- 

 ferred in all cases. 



Plate V. 



Fig. 1. Parmula Batesii. Perpendicular section of the statoblast through 

 the aperture, showing : — a, cavity tilled with germinal matter ; 

 b, coat enclosing the same ; c, chitinous coat ; d, crust ; e, inter- 

 nal layer of parmuliform spicides ; /, external layer of the same ; 

 g, minute spinous acerate spicules ; h, aperture ; i, nipple-like 

 prolongation of b. 



Fig. 2. The same. More magnified view of fragment of crust bearing 

 two parmuliform spicules : a, crust, to show granular appear- 

 ance of microcellular structure ; b, parmuliform spicule, end 

 view ; c, the same, lateral view ; d, more magnified view of 

 spinous acerate spicule. 



Fig. 3. Spongilla nitens, n. sp. Perpendicular section of the statoblast 

 through the aperture : a, cavity filled with germinal matter ; b, 

 coat enclosing the same ; c, chitinous coat ; d, crust composed of 

 columns of hexagonal cells in the section, in juxtaposition ; 

 e, inner layer of spinous acerates ; /, external layer of the same ; 

 g, aperture ; h, nipple-like prolongation of b ; i, more magnified 

 view of cell-structure of crust ; k, the same of spinous acerate. 



Fig. 4. S. naviceUa, n. sp. Perpendicular section of the statoblast 

 through the aperture ; a, cavity filled with germinal matter ; 

 b, coat enclosing the same; c, chitinous coat; d, layer or 

 capsule composed of minute navicelliform acerates (no ap- 

 pearance of crust-substance) ; e, aperture ; /, nipple-like pro- 

 longation oib; g, more magnified view of navicelliform spicule. 



