290 



MICROSCOPE. 



while the spicula of some are round at one end, and pointed 

 at the other acuate ; and also spicula round at one end, 

 the former being dilated into a knob spinulate; some 

 have a spinous surface. 



Fig. 173. 



1, Gemmules of Spongilla fluviatilis, enclosed in spicula. 2, Birotulate spi- 

 cula, from Flumatilis. 3, Gemmules of Spongilla fluviatilis, after having been 

 immersed in acid, to show its coating of birotulate spicula. 



From the South Seas specimens are found having spicula 

 with both ends rounded cylindrical ; some curved, others 

 straight. In an unclassed genus, the spicula are discovered 

 rather cylindrical in form, pointed at both ends, having 

 the surface covered with spines placed in an angular form 

 (fig. 169, No. 11), and another in which the spicula exhibit 

 many curious forms ; within the circle may be seen one 

 spiculum of remarkable beauty, being of large size, rounded 

 at both ends, and slightly bent; its outer surface is covered 

 with rows of tubercles of circular figure, which project 

 some little distance beyond the free margin. . In Hali- 

 chondria from New Zealand, there are found some with 

 the spicula of the acuate form covered with spines, blunt 

 at one end and sharp at the other ; the spines are small, 

 without order in their situation, but greater in number at 

 the middle. In the genus Packymatisma some spicula are 

 sharp at one extremity and expand into two points at the 

 other expando-binate ; they are large, and their purpose 

 is that of connecting the crust and the fleshy matter com- 

 pactly together. The P. Johnstonia spicula are sharp at 

 one end and expand into three points at the other 



