OF THE SPONGIAD^. 271 



ANATOMICAL STRUCTURE OF SP1CULA. 



FIG. 



247. Distal termination of a porrecto-ternate spiculum from 



TetJtea cranium, with angular distortions from ex- 

 ternal pressure. X 260 linear. Page 6. 



248. A portion of an adult spiculum from Spongilla 



fluviatilis, charred to exhibit the thin membrane 

 of the central cavity of the spiculum. X 260 

 linear. Page 6. 



249. A portion of an immature spiculum from Spongilla 



lacustris, charred to exhibit the dense membrane 

 lining the large central cavity in the young spicu- 

 lum. X 260 linear. 



250. A section at right angles to the axis of the upper 



part of the shaft of a ternate spiculum from Geodia 

 Barretti, Bowerbank, MS., exhibiting the concen- 

 tric layers. X 260 linear. Page 6. 



251. 252. Portions of charred spicula from the skeleton 



fasciculi of Tethea cranium, exhibiting their hol- 

 low condition after incineration. X 90 linear. 

 Page 8. 



253. A portion of a spiculum from Euplectella aspergillum, 



Owen, slightly charred, exhibiting the concentric 

 layers of silex. X 90 linear. Page 11. 



254. A portion of an adult spiculum from the skeleton of 



Geodia McAndrewii, Bowerbank, MS., cracked by 

 the application of cold water while in a heated 

 state. X 90 linear. Page 9. 



MEMBRANOUS TISSUES. 



255. FIBRO-MEMBRANOUS TISSUE. Containing a single layer 



of parallel fibres on a portion of the membrane 

 from an excurrent canal of one of the common 

 honeycomb sponges of commerce. X 660 linear. 

 Pages 67, 99, and 100. 



