1887.] NATURAL SCIENCES OF PHILADELPHIA. 273- 



Explanation op Plates. t 



The magnification used in plates V. and VI. is irregular, as 

 suited the several subjects of the artist. The figures on plates 

 VII to XII inclusive, are uniformly magnified about 200 times 

 and represent the spicules as seen upon prepared slides. 



Plate V. 



Fig. I. Spongilla lacustris. Surface of gemmule showing,-a, posi- 

 tion and character of "infundibular" foraminal aperture ; 

 b, acerate gemmule spicules, lying upon, or imbedded in,, 

 a granular "crust." (See PI. VII.) The position of these 

 greatly varies in the different "varieties" or "forms," gov- 

 erned generally by the thickness of said "crust." 



Fig. II. Spongilla fragilis. A, upper surface of part of "pavement 

 layer" of gemmules ; a, foraminal tubules, mostly curved, 

 located at the centre of the upper surface of each gem- 

 mule; h,h, acerate spicules embedded in the "cellular paren- 

 chyma" which surrounds and combines the gemmules. 

 (See PI. VIII.) B, section of "group" of "errant" gem- 

 mules ; a, curved foraminal tubules, ahvays outivard ; b, 

 envelope of cellular parenchyma charged with acerate 

 spicules. 



Fig. III. Spongilla igloviformis. A, "elevation" of dome-shaped 

 group of gemmules, showing through the surface of the 

 "cellular parenchyma" which has been made transparent, 

 the several gemmules in position, surrounded by the echin- 

 ating acerate "parenchyma spicules." (PI. VIII, fig. v.) 

 , the surface (transparent) of a similar group as seen 

 from above. The foraminal apertures, not here visible, all 

 open inward. 



Fig. IV. Meyenia leidyi. A, upper surfiice of portion of a layer 

 of gemnailes, each of wliich, besides its "blrotulate" ar- 

 mature, (PI. X, fig. i.) (not shown in this sketch) is sur- 

 rounded by-c, a "lattice capsule" of spicules resembling 

 those of the skeleton ; at the summit of which an open 

 space occurs, around-a, the foraminal aperture ; more 

 than one being sometimes present. B, section of part of 

 "chitinous coat" of a geinmule, showing (imperfectly)-^,, 

 its armature of blrotulate spicules in position. 



