192 ANATOMY AND PHYSIOLOGY 



great mass of the species of Hymeniacidon, and I accord- 

 ingly inserted them in the list of British sponges, published 

 in the " Report of the Dredging Committee" in ' the Reports 

 of the British Association' for 1860, under the titles of 

 Halina suberea, ficus, &c. ; but a closer examination of 

 their internal structure has convinced me that their only- 

 real difference from the other species of Hymeniacidon is 

 in their greater compactness of skeleton structure, and 

 I have accordingly repaoved those species to the genus 

 Hymeniacidon. 



In the greater number of the species of this genus the 

 tension spicula are of the same form as those of the skeleton, 

 and are only to be distinguished from them by their greater 

 degree of tenuity, but in a fevr of the known species they 

 are different both in size and form. 



The mode of propagation in all the species in which I 

 have found the reproductive organs, appears to be by 

 internal gemmulation. In H. carnosa and several other 

 species of the genus they are simple, spherical, aspiculous, 

 membranous vesicles, filled with round or oval vesicular 

 molecules. The genus Halisarca, Dujardin, was supposed 

 by both that author and Dr. Johnston to be entirely des- 

 titute of spicula ; but I have, since the publication of the 

 ' History of the British Sponges,' found them in H. Du- 

 jardinii in abundance. They are so minute and so com- 

 pletely obscured by the surrounding sarcode, that they can 

 rarely be detected in either the living or the dead specimens 

 when examined in water ; but if a portion of the sponge be 

 dried on a slip of glass and covered with Canada balsam, 

 they may be detected by transmitted light and a power of 

 400 linear in considerable numbers, dispersed on the inter- 

 stitial membranes of the sponge. This genus will therefore 

 merge in that of Hymeniacidon, with which it agrees in 

 every structural peculiarity. Fig. 373, Plate XXXV, 

 exhibits the dispersed condition of the skeleton spicula on 

 the interstitial membranes of a specimen of Hymeniacidon 

 carimcula, X 108 linear. 



