10 Spong . 
SPONGLflC. 
gradation, showing how a siliceous skeleton with scarcely any spongin 
may be replaced by a horny skeleton with only a trace of spicules. 
Hence, it can scarcely be doubted that some horny Sponges, at least, are 
descendants of siliceous Chalinince. 
Fol finds that the filaments of Ilircinia are an integral part of the 
Sponge. They arise from bands of fusiform cells, evidently belonging to 
the connective tissue of the Sponge, which atrophy after producing the 
fibril. 
Yon Lendenpeld (10) gives a description of the chones in the genus 
Stelletta (pp. 61 & 62). 
Perrier & Schimk^witscii discuss the zoological position of Sponges 
as a class, arriving at very opposite conclusions. 
Topsent (4) has found that in cutting specimens of Pachymatisma 
johnstonia , Bwk., it was often possible to dissect away and extract from 
the large efferent canals a ramified, system of whitish tubes, opening to 
the interior by as many openings as the specimen had oscula. This 
was due to a partial breaking away of the walls of the efferent 
canals. 
Topsent (6) describes very thoroughly the anatomy and histology of 
some species of the genus Cliona , and of a number of Renierince belonging 
to the genera Reniera , Amorphina , and Dendoryx. In all these forms he 
finds four kinds of cellular elements : — (1) Contractile cells, under which 
category are to be included the elements which have been termed cells of 
the ectoderm and endoderm, fibrous cells, or contractile mesoderm cells. 
These cells clothe the walls of the canals and occupy all points where 
alternate contraction and relaxation is necessary. Where this is not the 
case they may be replaced by a cuticle. (2) Vibratile cells (collared 
cells) ; in Cliona the colls aro united to ono another by their collars. 
(3) Connective tissue cells, actively amoeboid, and united to neighbouring 
cells by their pseudopodia. They often contain reserve material. (4) 
Pigmented digestive cells, which are amoeboid and ingest food particles ; 
these are also the reproductive cells, and become ova or spermatozoa. 
(1) and (2) constitute the ectoderm and endoderm, (3) and (4) the meso- 
derm. The author has also observed these four kinds of cell elements in 
other siliceous Sponges (p. 122), and believes that all Silicosponges have 
the same histological composition. 
Cliona celata is investigated in its three forms, the boring, incrusting, 
and raphyroid (= Raphyrus grijfithpii , Bwk.). The author finds in the 
genus Cliona , typically, three kinds of spicules, for which Bowerbank’s 
terms, “ essential skeletal spicula,” “ tension spicula,” and “ spicula of the 
membranes” are used. Only one or two of these three kinds may be 
present. Use is made of their modifications for sub-dividing the genus 
Cliona. [ Vide infra , Systematic.] 
After a summary of former views as to the affinities of the Clionidce, 
the author concludes that they are true Corticatcx, and form in this 
group a natural family of equal importance with lethyadee , Ancorince, or 
Geodice. 
