322 



NATURAL HISTORY. 



Besides the foregoing lai'ge spicules, which, as a rule, form the chief skeleton of the Sponge, 

 other much smaller ones exist (Fig. 11), which, because they are seldom united into a coherent 

 skeleton, but occur dispersed throughout the mesoderm, have been termed flesh spicules, a term not 

 unopen to objection. Many of these simply repeat the forms of the large spicules, but altogether 

 they present a greater diversity and frequently also a greater complexity of form. The minute 

 acerate () by curvilinear growth becomes tricurvate (6) or bow-shaped, or hamate (c and d), or 

 sinuate (e) ; the sinuate, if spined all over, is a spini-spirula (e) ; and from this we seem to pass to a 

 straight spicule with whorls of spines (sceptrella, </), or to a spined globule (globostellfUe, Fig. 10, ). 

 The C or bow-shaped spicules, by various modifications of their ends, give rise to various forms 



Fig. 1 1 . VARIOUS SMALLER FORMS OF SPONGE SPICULES. (After Bowerbanfc, Schmidt, Sollas, and others.) 



known as anchorates (h, k), distinguished as equi-anchorates, if the ends are equal and similar (A, t), 

 inequi-anch orates, if one is smaller than the other (f, j). The inequi- anchorates are sometimes 

 clustered together into radiate groups, the small ends meeting at the centre, and the larger diverging 

 at the margin. Rosettes of remarkable beauty (o) so produced are common in Esperia. The 

 small spicules of the Hexactinellidw are, like the large, characteristically sex-radiate ; they may be 

 regularly and simply six-rayed (m), or the rays may divide into two, three, or more straight or 

 curved secondary rays, the ends of which may be pointed or capitate (p, q). The anchorates (k) of 

 this group are represented by a form which is not obviously sex-radiate ; it consists of a central 

 shaft with eight re- curved arms at each end ; it sometimes is found in rosettes like the inequi- 

 anchorates of Esperia. In this group occurs a nail-like spicule, with a cruciform head, the shaft 

 of which is covered with large spines, all pointing towards the end ; these " wheat-sheaf " spicules (n) 

 adorn the margins of the oscules of Meyeria, the heads being embedded in the skin and the 

 points projecting into the oscule. The broom-shaped spicules shown in the figure (I) are charac- 

 teristic of some Hexactinellids. 



Finally, various forms of multi-radiate small spicules are plentiful, the simplest of which 

 consists of a number of fine, hair-like rods (trichites), developed in a fasces-like bundle (trichite 

 sheaf), within a single cell (s, t). In other forms, the trichites grow radiately outward from a 

 common centre, and, becoming thickened with age, produce a trichite-stellate, or, if they are very 

 numerous, a trichite-globate or globate spicule (r, u). The globate is characteristic of the most highly 

 developed and complicated of ail Sponges, viz., the Geodina. It commences as a minute ball of 

 trichites, the inner ends of which are fused into a little globule at the centre. It is developed 

 within a single cell, with a large nucleus (u), and, as it grows, the trichites becoming longer and 



