37 



(PI. iii. fig. 12, a) I observed in some of the vessels numerous minute 

 globules, exhibiting every appearance of being globules of circulation 

 analogous to those found in the blood of the higher classes of animals. 

 They are circular, and vary in size from each other to about the same 

 extent that the blood-discs in man and animals do. The largest of 

 these globules was r6 | 66 of an inch in diameter, the smallest ro S 00 

 of an inch. The mean diameter of the vessels was 93 l 6 of an inch j 

 and the fibre of the sponge upon which they ran was yf^ of an inch 

 in diameter. 



A similar vascular tissue exists in a considerable number of the ke- 

 ratose sponges from Sydney ; in some it is as distinctly apparent as 

 in the Turkey sponge (as in fig. 13), while in others, although equally 

 abundant, it is scarcely to be distinguished from the horny mass of 

 the fibre. In some of the Australian species, where it is extremely 

 well developed, the centre of the horny fibre abounds in spicula. In 

 some specimens of Spongia officinalis also, there are faint traces of 

 a similar tissue occasionally to be seen. Upon making sections of 

 small cylindrical bundles of the Australian species, in the manner be- 

 fore described, and viewing them as opaque objects with a power of 

 500 linear, and with the aid of a Lieberkuhn, they proved to be of as 

 solid a texture as the sponges of commerce : no indication of a cavity 

 existing in the fibre being apparent, excepting where spicula had 

 been formerly imbedded, and which had been displaced by the pas- 

 sage of the knife. The only truly tubular sponge that I have yet seen 

 is Spongia fistularis, described by Dr. Grant in one of his papers in 

 the ' Edinburgh New Philosophical Journal.' I am indebted to the 

 learned Professor for a specimen of this interesting species, he having 

 kindly shared with me the few remaining fibres in his possession. 

 Upon examining these, immersed in water, with a power of 500 linear, 

 I found the interior of the horny filaments to be truly tubular. The 

 filaments, unlike those examined by Dr. Grant, were quite empty, 

 no dark granular matter being visible ; and in several of them I saw 

 the air gradually expelled by the entrance of the water, thus proving 

 the truth of their tubular nature beyond a doubt. I cannot take leave 

 of this subject without a few observations on the nature of the spicula 

 which are found in such abundance in these curious bodies. 



Professor Grant, in his * Outlines of Comparative Anatomy,' p. 5, 



Ship, whose skill in the injection of fine vascular tissues is so well known, has succeeded 

 in filling these minute vessels with coloured pigments, in the most complete and satis- 

 factory manner. 



