AND PHYSIOLOaY OP THE SPONGIAD^. 
membranes, each consisting of simple interstitial membrane with a layer of primitive 
fibrous tissue beneath it ; the fibrous portion consisting of a single series of fibres 
parallel to each other, and so closely adjoining as to touch each other through nearly 
their whole course (Plate XXVII. fig. 4). 
When the fibres are clear of the membranous tissue they appear as simple pellucid 
threads, but when covered by the membrane they frequently appear as if moniliform ; 
this character seems to be due to minute molecules arranged in linear series on the 
membrane immediately above them. These membranes abound in large open oval 
spaces, so that the tissue assumes very much the appearance of areolar tissue, as 
described by Professor Bowman in his treatise on mucous membrane in the ‘ Cyclopaedia 
of Anatomy and Physiology.’ 
The layer of membrane forming the surface of the canal has its fibres disposed at 
right angles to the axis of the canal, while those of the layers beneath it assume various 
directions, usually in straight lines, excepting in the vicinity of the areas of communica- 
tion, around which they curve to strengthen their margins. 
In the canals deeply buried in the mass of the sponge, the sides frequently consist of 
but one layer of membrane and primitive fibrous tissue, and in this case also the fibres 
are always disposed at right angles to the axis of the canal, but they are neither so 
numerous nor so closely packed as in the sides of the great excurrent canals. 
The interstitial membranes are also furnished with these fibres, sometimes in consider- 
able quantity, but rather irregularly disposed, while in other cases a single fibre only 
will be observed meandering across the tissue. 
The interstitial membranous tissues in a beautiful little specimen of Alcyoncellum 
from the North Sea, for which I am indebted to my friend Captain Thomas of the Hydro- 
graphical Survey, are very similarly constituted to those of the sponges of commerce. 
The membranous walls of the interstitial cavities are each formed of a series of fibro- 
membranous layers, the fibres of each layer being disposed at angles varying from those 
above and below it. 
Figures 1, 2, 3, & 4, Plate XXVII. represent portions of the lining membranes of 
the incurrent and excurrent canals, and the mode of the disposition of the primitive 
fibrous structure upon them. 
Intermarginal Canities. 
In the Halichondroid sponges, immediately beneath the dermal membrane, there are 
numerous and, comparatively speaking, large irregularly formed cavities which receive 
the water inhaled by the pores, and convey it to the mouths of the incurrent canals, 
which have their origin in the deepest portions of the spaces. These organs, from their 
irregularity in size and form, are not always very apparent ; but if a section be made at 
right angles to the surface in a dried specimen of Ilalichondria 'panicea or Hal. simulans., 
Johnston, they may be readily detected and distinguished from the interstitial canals 
and spaces of the sponge. 
Fig. 13, Plate XXXI. represents a section of Ilalichondria panicea., and fig. 1, 
MDCCCLXn. 5 p 
