112 M. E. lliickel 071 tJic Organization of Sponges, 



there is produced in tlie interior of this vibratile embryo a 

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

 tlirongh to the outside, accpiires an oritiee (moutli). As has 

 ah-eady been remarked, the wall of tliis simj)le stomachal 

 cavity (body-cavity) then becomes ditfcrentiated into two 

 difterent cellular layers. After the vibratile larva has issued 

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

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

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

 contrary, those cells which surround the stomachal cavity emit 

 each a tiliform ])rocess, and thus become flagellate cells and 

 form the entoderm. It is only much later, when the s])onge 

 has attained its true nu\turity, that the s})ores 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 with a mouth -orifice, is 

 composed, in the smaller Calcispongiaj (e. g. Olgntlnn^, Nar- 

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

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

 Calcispongiffi, on the contrary (e. g. Dunstervillia, Olathrina)^ 

 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. T/ie ectoderm consists of intimately 

 amalgamated naked cells, the nuclei of which are always 

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

 the united protO})lasm, which is frequently differentiated in 

 various ways. The nuclei are generally of an elongate- 

 rounded form, and frequently surroundetl 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 Caleispongia3, 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 originallg separated cells hy their subsequent fusion , 

 as is clearly ])rove(l by the ontogeny of the embryos and 

 larva3. The ectoderm therefore does not merit the name of 

 true sarcode, if under this notion we understand free and jjri- 

 mitive 2irotoj)lasm not get differentiated into cells. The deno- 

 mination syncytium or sarcodine might perhaps seem more 

 suitable for it. 



