. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. sponge. These spicula, which are composed of pure , are generally united into fasciculi by an enveloping glutinous or condensed cel- lular substance, and by the junction of these fasciculi in various modes fibres are formed, which traverse every part of the body, form- ing the boundaries of canals and orifices, and giving form and support to the whole of the gelatinous or soft cellular substance of the animal.* The spicula, so far as the British species are concerned, Dr. Johnston observes, seem to be always in the
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. sponge. These spicula, which are composed of pure , are generally united into fasciculi by an enveloping glutinous or condensed cel- lular substance, and by the junction of these fasciculi in various modes fibres are formed, which traverse every part of the body, form- ing the boundaries of canals and orifices, and giving form and support to the whole of the gelatinous or soft cellular substance of the animal.* The spicula, so far as the British species are concerned, Dr. Johnston observes, seem to be always in the shape of simple needle-like crystals (fig. 70) ; nor does any Fig. 70. Single interspace or open cell, and surrounding finer mesh-work of the skeleton of Euplectella Aspergillum. (After Owen.) living cortex. The horny threads composing this inextricable labyrinth are of unequal thickness, and by some writers have been erroneously described as being throughout tubular; but this latter is a mistaken view of their structure, dependent upon optical ap- pearances, as has been proved by Mr. Bovver- bank * and others, the horny fibres being, in fact, solid and imperforate. In a second group of Sponges, called Halichondria (xaAi?, silex; x°"5/'°y> carti- lage), the solid framework of the bodv is principally made up of silk-ions spicula, im- bedded in the fibre or parenchj ma of the * Microscopic Journal, vol. i. p. A minute film of the rind of Tethea Lyncurium com- pressed between plates of glass, and highly magnified to show the needle-like and starred spicula. (After Johnston.) species present us with spicula of two differ- ent forms, though thev sometimes vary much in length and gracility ; but he cannot assent to the opinion of Dr. Grant that the form is different in every distinct species, otherwise the task of distinguishing them would be com- paratively A third group of Sponges, designated by Blainville, Calcespongia, has the framework which gives them
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