1112 
DE. J, S. BOWEEBANK ON THE ANATOMY 
of the genus the gemmules 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 destitute of spicula; but I have, since 
the publication of the ‘ History of the British Sponges,’ found them in H. Dujardinii 
in abundance. They are so minute and so completely 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 interstitial membranes of the sponge. 
This genus will therefore merge in that of Hymeniacidon^ with which it agrees in every 
structural peculiarity. Plate LXXIV. fig. 6. 
Suborder III. Spiculo-reticulate skeletons. Skeletons continuously reticulate in struc- 
ture, but not fibrous. 
Halichondria. 
Hyalonema. 
Isodictya. 
Spongilla. 
The sponges of this suborder vary in the different genera to a great extent in the 
mode of the construction of the skeleton, but in all cases the spicula are the dominant 
material; their terminations overlap each other, and they are cemented together by 
keratode. The reticulations thus formed sometimes consist of a single series of spicula, 
at other times they are very numerous and are crowded together in the manner of 
elongated fasciculi. 
The genera Halichondria and Isodictya are exceedingly rich in species ; but the incon- 
venience attending their discrimination, arising from their number, may be remedied to a 
great extent hereafter by subdivisions of each genus, based on the characteristic forms 
of the spicula of their respective skeletons. The structural distinction between Halichon- 
dria and Isodictya is so well marked as to render the recognition of each comparatively 
certain and easy. The skeletons of the species of the latter genus, generally speaking, 
are very much more slight and fragile than those of the former one ; and the same rule 
obtains to a great extent as regards the comparative size of their spicula, and in many 
species of Isodictya they are very minute. Hyalonema and Spongilla are readily to be 
distinguished by the peculiarities of their structure and localities. 
The genus Halichondria as constituted by Dr. Fleming in his ‘ History of British 
Animals,’ and adopted by Dr. Johnston in his ‘History of British Sponges,’ contains 
species which differ exceedingly in their mode of organization. Thus, if we take 
H. panicea of Johnston, which is undoubtedly the “sponge-like crumb of bread” of 
Ellis and the older authors, and therefore the proper type of the genus, we find the 
skeleton destitute of fibre, but composed of an irregular network of spicula cemented 
together at their apices by keratode. If we examine the well-known branching sponge 
