112 M. E. Hackel on the Organization of Spo7iges, 



there is produced in tlie interior of this vibratile embryo a 

 central cavity (stomach), which, sooner or later breaking 

 through to the outside, acquires an orifice (mouth). As has 

 already been remarked, the wall of this simple stomachal 

 cavity (body-cavity) then becomes diiferentiated into two 

 different cellular layers. After the vibratile larva has issued 

 from the parent body, and come to rest after swimming about 

 for a time, the cells of the outer surface retract their flagella, 

 become fused together, and thus form the ectoderm. On the 

 contrary, those cells which surround the stomachal cavity emit 

 each a filiform process, and thvis become flagellate cells and 

 form the entoderm. It is only much later, when the sponge 

 has attained its true maturity, that the spores are produced 

 from individual cells of the entoderm. 



The body-wall, or stomachal wall of the freely swimming, 

 ovate, vibratile larvae, the entire canal-system of which con- 

 sists of a simple stomachal cavity Avith a mouth-orifice, is 

 composed, in the smaller Calcispongiaj (e. g. Oli/nfhus, Nar- 

 doa), only of two layers of cells, the ectoderm and the ento- 

 derm each forming only a single layer of cells. In the larger 

 Calcispongiaj, on the contrary (c. g. Dunstervillm, Chithrina), 

 each of the two sets of cells may divide into several layers. 



The ectoderm or outer formative membrane of the Calci- 

 spongice^ produced from the outer cell-layer or animal germ- 

 lamella of the embryo, always forms more than half the 

 volume of the body, as it is always thicker (often several 

 times) than the entoderm. The ectoderm consists of intimately 

 amalgamated nahed cells, the nuclei of which are always 

 at first, and usually even at later periods, distinctly visible in 

 the united protoplasm, which is frequently diiferentiated in 

 various ways. The nuclei are generally of an elongate- 

 rounded form, and frequently surrounded by an aggregation 

 of fine granules, which not rarely radiate from the nucleus 

 and extend in various directions into the protoplasm. Al- 

 though in the ectoderm of the mature Calcispongiaj, the appa- 

 rently almost homogeneous, nearly structureless, fundamental 

 substance, charged with nuclei and skeletal spicules, no longer 

 allows any trace of the amalgamated cells of which it is com- 

 posed to be recognized, it has nevertheless been actuallg pro- 

 duced from originally separated cells by their subsequent fusion^ 

 as is clearly proved by the ontogeny of the embryos and 

 larvae. The ectoderm therefore does not merit the name of 

 true sarcode, if under this notion we understand free and j:)r/- 

 mitive protojylasm not yet differentiated into cells. The deno- 

 mination syncytium or sarcodine might perhaps seem more 

 suitable for it. 



