474 
PROTOZOA. 
Esp. j Tragoaia calmfonnis, Esp. (mfimdibulifortnis, Bow.); Reuiora {Scftmtd- 
tUi) clavatUf Esp. ; Myrmekioderma (g. n.) granulatum, Esp. ; Spongia lyco- 
podium, Esp., is an Alya with a parasitical sponge. 
Anatomy and Physiology. 
IIackel’s Calchpongia ” (14) puts in the shade all papers hitherto pub- 
lished on these organisms ; and, surprising as many of the results brought for- 
ward in it may appear, they seem to be, on the whole, borne out by facts, 
leaving little room for criticism, at least until new investigations are on 
record. The following is a sketch of the general organization of calcareous 
sponges as now known, chiefly through this author’s researches. 
The Morula ” stage of the embryo is succeeded by the Planida stage, the 
oval fimbriated sponge-larva, the body of which is composed of two cell- 
layers — an inner of roundish or polygonal nucleated cells, the mdodenn, cor- 
responding to the inner germ-plate of the embryo of higher animals ; and 
an outer of elongate, prismatic, nucleate, flagellate cells, the exoderm, homo- 
logous with the outer germ-plate. After the development of a gastric cavity 
in its interior, and its opening into a mouth, the is a Gastrula ; ” 
when fixed by its aboral extremity, the flagella of the exoderm are with- 
drawn, and the colls themselves fused together into a syncytium,'^ while 
the endodermal cells are, on the other hand, transformed into flagellate 
colls. This stage is termed the ^^Ascula,” and passes into the “ Protosponyia ” 
state by the formation of transitory pores perforating the body-wall and 
establishing water-currents through the motions of the flagella of the endo- 
derm. When calcareous spicula are formed in the exoderm, the young 
sponge is an “ Olynthus” the simplest type of the Ascones, and hence of all 
Grantice ” or Calcispongice — a cylindrical, clavate or pyriform &c. tube, 
closed at the extremity by which it is affixed, commonly open by a mouth ” 
at the other; the body-wall, enclosing the “ gastric ” cavity, is a thin mem- 
brane composed of the two layers named above — the “ syncytium ” or exo- 
derm, a mass of sarcodine with nuclei, the cells of which are so completely 
fused together that the original cellular structure cannot be made visible 
through any chemical reaction; if torn mechanicall}’^, the fragments will, 
whether containing one or more or no nuclei, take the shape of Amoehce 
and walk about. In this layer the spicula are developed, chiefly of three 
types — simple, 3-radiate, and 4-radiate; anchor-shaped spicula are rare 
{Syculmis synapta, anchoring the animal in the mud bottom) ; the stellate 
spicula sometimes occurring are foreign bodies, belonging originally to 
Didemna {Ascidice). The spicula are invested with a delicate sheath of 
condensed sarcodine ; they contain an axial filament, and are composed of 
concentiic layers, like the siliceous spicula ; chemically they are composed 
partly of 00^ CaO, partly of an organic substance (^‘ spiculin ”). The en- 
dodermal cells are, like certain flagellate Infusoria, provided with a collar 
and flagellum ; they contain a nucleus ” (with “ nucleolus ”), and often one 
or two contractile “ vacuola ” (water-drops) ; though without mouth,” 
they both drink ” and “ eat,” or receive into their interior, not only fluid 
but also minutely diffused solid matter (e. g. carmine), probably through the 
soft exoplasm between the collar and flagellum. Liberated artificially they 
also assume amoeboid shape and motions. On the endodermal cells devolve 
