THE FKESH-WATER SPONGE. 
137 
sidered that a Fourth Kingdom was not desirable.* Yet some of 
our own distinguished naturalists at the present day maintain a 
Fourth or a Sub Kingdom ; and I may add that after a lapse 
of eight years since that paper was written, I am more satisfied 
with its desirableness and utility, and feel assured that after 
further consideration of the extreme difficulties of the primary 
questions of biology a Fourth Kingdom of Nature will be gene- 
rally adopted. Keference may also be made to my last published 
notice on the sponges, which is a letter in the “AthenaBum” for 
1867, p. 160; and I cannot pass over Dr. J. E. Grray’s useful 
Notes on the Arrangement of Sponges, with the Descriptions 
of some New Grenera,” just published in Part II. pp. 492-558, 
‘^Proceedings of the Zoological Society” for 1867. 
I must now proceed to mention briefly some of Professor 
Williamson’s accounts of the Spongilla fluviatilis. With re- 
gard to “the labours of Mr. Carter,” which are contained in 
several numbers of the “Annals and Magazine of Natural His- 
tory,” I cannot place as much reliance on them as some others 
have done, for many of his details are so contradictory, prolix, 
and uncertain, that it is difficult to ascertain his real views 
and the distinct facts of his observations. 
Professor Williamson only detects three elements in the Sjpon- 
gilla, viz. first, “the investing jelly,” which I have termed 
(See Lin. Trans, vol. xviii. p. 387, 1840) “the parenchymatous 
substance,” now called by those who consider the organism to 
be an animal, “ sarcode.” But sarcode is more correctly ap- 
plied, as originally by De Blainville, to certain polypes — 
“ Sarconoides ” — Sarcoidea, which has the same meaning as 
Lamouroux’s “ Carnoides,” and which is given to the polypi- 
ferous fiesh, or “ carnode,” or mner substance of the Alcyonia, 
Lobularise, &c., and which are admitted by every one to be true 
animal substances. Second, the “ internal skeleton,” consisting 
of anastomosing fibres with bundles of brittle spicula composed 
chiefly of sllex ; and third, the round “ seed-like bodies.” To 
these I will add a fourth element, namely, the transparent 
“ investing membrane,” or the “ diaphanous pellicle ” of Dr. 
Johnston, which envelopes the entire mass, and lines all the 
inner pores and oscules. 
The Professor seems to place great dependence upon the ob- 
servations of Lieberkuhn with regard to the Spongilla, This 
Grerman naturalist’s memoir is of more recent date than my 
own notices on the same organism, which were published in 
1840, in vol. xviii. of the “ Linnsean Transactions.” Lieber- 
kuhn’s remarks, printed in Muller’s “ Archiv,” 1856-7, are un- 
fortunately not written in Latin, or in French, and being filled 
with abstruse technical terms and phrases are only compre- 
hensible by those scientific persons well acquainted with the 
