36 



ject them to this test, the difference becomes at once apparent. The 

 mode of arrangement and size of the fibre of the new species is very 

 similar to that of the former one, and the large irregularly formed tis- 

 sue containing spicula occurs as frequently as in Sp. officinalis. The 

 striking character in this species is its possession of a beautiful vascu- 

 lar tissue, wliich surrounds, in great abundance, nearly every fibre of 

 its structure ; which, when it is immersed in water and viewed as a 

 transparent object with a power of 500 linear, presents the appearance 

 represented at figs. 11 and 12 PL iii. where the vessels are seen mean- 

 dering over the surface of the fibres in every direction. Sometimes 

 they proceed for a considerable distance in a line nearly parallel to 

 the axis of the fibre, giving off frequent lateral branches at right an- 

 gles, some of which terminate immediately in cceca, while others em- 

 brace half or two thirds of the diameter of the fibre before they ter- 

 minate; other branches thus given off continue their course for a 

 considerable distance, either running parallel to the parent vessel, or 

 passing in spiral lines round and round the fibre ; the direction of the 

 spire sometimes being from right to left, and at others from left to 

 right. Occasionally they expand to twice their original diameter, and 

 again contract to their former size. This beautiful tissue is not im- 

 bedded in the horny mass of the fibre, but is contained in a sheath, 

 which closely embraces it, and it frequently occurs in the preparation 

 of a fragment of the sponge for examination, that the horny fibre is 

 withdrawn from this sheath, leaving it in the form of a thin membra- 

 nous tube, in the substance of which the vascular tissue is imbedded. 

 Fragments of the vascular coat are also often seen partly adhering to 

 the fibre from which they have been torn. The vessels are completely 

 imbedded in the sheath which contains them, as no projection of their 

 surface appears when they pass round the fibre. It might at the first 

 view be imagined that they were merely excavations or canals in the 

 substance of the sheath surrounding the horny fibre, but this is proved 

 not to be the case, by their often being torn out from the substance in 

 which they are imbedded, and exhibited as a detached network. So 

 in like manner it might be thought they were but a tissue of solid fi- 

 bres imbedded in the outer coat of the structure ; but their tubular 

 character is established by the frequent occurrence of alternations of 

 air and water within their cavities. Little doubt therefore can remain 

 of their being a true vascular tissue, destined to perform an important 

 office in the economy of the animal during its life.* In one instance 



* Since this paper was read, my friend Mr. G. Busk, of the Dreadnought Hospital 



