OF THE SPONGIAD^I. 243 



SPICULA OP THE MEMBRANES. 



TENSION SPICULA. 



FIG. 



90. FUSIFORMI-ACERATE : ENTIRELY SPINED. X 660 



linear. This form of spiculum occurs abundantly 

 in the dermal and interstitial membranes of Spon- 

 yilla lacustris, Johnston. Pages 38, 42, and 58. 



91. PUSIFORMI-ACERATE : TRUNCATEDLY SPINOUS. X 660 



linear. Abundant in Spongilla alba, Carter, in 

 both the dermal and interstitial membranes. Page 

 42. 



92. MUCRONATO - CYLINDRICAL. X 400 linear. The 

 dermal membrane of Halichondria incrustans, 

 Johnston, is abundantly furnished with large flat 

 fasciculi of this form of spiculum. They are as 

 long as those of the skeleton, but not above half 

 their diameter ; they are entirely destitute of spines, 

 while the spicula of the skeleton are covered with 

 those organs. Page 40. 



. TERMINALLY SPINED SUBFUSIFORMI-CYLINDRICAL. 

 This form of spiculum is abundant in the dermal 

 membrane of Halichondria niyricans, Bowerbank, 

 where it occurs in irregular fasciculi. It is as long 

 as the spicula of the skeleton, but has not quite 

 so great a diameter, and is distinctly different in 

 its form. 



93. TUBERCULATED FUSIFORM1-CYLINDRICAL. X 660 



linear. These minute spicula are profusely dis- 

 persed on the inner surface of the dermal and inter- 

 stitial membranes of Pacliymatisma Johnstonia, 

 Bowerbank. They are covered very irregularly 

 with ill-defined tubercles. They vary very con- 

 siderably in form and proportions. Their average 

 dimensions are, length g^th inch, diameter 

 inch. Page 42. 



