80 ANATOMY AND PHYSIOLOGY 



dilation is very strongly produced, as represented in a few 

 fibres of Bactylocalyx Prattii, Bowerbank, MS., Fig. 276, 

 Plate XV. 



Of the second form, simple fistulose siliceous fibre, I know 

 but one example, and that is the remains of the siUceo- 

 fibrous sponge, Farrea occa, Bowerbank, MS., on which 

 the beautiful specimen of Euplectella cucumer, Owen, is 

 based. 



The tubulation of the skeleton-fibre is very similar to 

 that of some varieties of simple fistulose keratose fibre, but 

 the central cavities are not so invariably continuous as in 

 the keratose varieties of fistulose skeleton-fibre. Fig. 277, 

 Plate XV, represents a small piece of the spinulated simple 

 fistulous fibres of the skeleton of Dr. Arthur Farre's speci- 

 men. The spinulation of these fibres is a remarkable cha- 

 racter. It is the only case of the production of acute spines 

 on the skeleton-fibre of a siliceo-fibrous sponge with which 

 I am acquainted. 



Prehensile Fibres. 



In the course of my examination of the fibrous skeleton- 

 tissues, I have found but one instance in which they have 

 developed prehensile organs to assist in the attachment of 

 the sponge, and this in a minute siliceo-fibrous species, 

 parasitical on the base of a specimen of Oculina rosea, from 

 the South Sea. In this sponge the basal fibres curve down- 

 ward in the form of numerous small, nearly semicircular 

 reversed arches, from the lowest portions of each of which 

 there is a short stout portion of fibre projected, and at 

 about the length of its own diameter downwards a ring of 

 stout prominent bosses, six or eight in number, is produced, 

 very considerably increasing its diameter at that part ; im- 

 mediately beneath which the fibre is attenuated to a point. 

 These singular organs are admirably calculated to penetrate 

 the porous cavities or fieshy envelopes of the coral, and 

 thus to securely attach the sponge to its adopted matrix 

 (Fig. 278, Plate XV). 



