14 Coelenterata. 



racteristic of each species of Par. Calcareous sand grains may predominate in one 

 species, sponge spicules in another, while both may be present in a third. In P. 

 tunicans the sand grains are found near the boundary of the ectoderm and meso- 

 glffia, while the sponge spicules are in the deeper layers of the mesogloea. The 

 size of the colonies and the extent to which ccenenchyme is developed are likewise 

 features of importance in Par. : in monostichus there is very little connecting coe- 

 nenchyme, while in tunicans hundreds of polyps are inserted in a common encrust- 

 ing ccenenchyme. All the members of a colony are of the same sex. 



Gardiner describes the anatomy of a supposed new species of Coanopsammia. 

 There are 48 mesenteries (12 primary, 12 secondary, 24 tertiary). From each 

 intermesenterial space a canal is given off which passes outside the theca. The 

 arrangement of the canals near the top of the theca, joining the intermesenterial 

 spaces with the corresponding coenosarcal canals alone, strongly supports the view 

 that in this species the theca is formed simply by the fusion of thickenings on the 

 sides of the septa. Lower down in the polyp, instead of separate connecting canals, 

 there is a system of ramifying and anastomosing canals. The canals at the free edges 

 of the colony end blindly, those in the central part put the polyps in communica- 

 tion. Budding takes place from the blind ends of the canals at the basal margin 

 of the colony. The tentacles are entocoelic, their 3 orders corresponding to the 3 

 orders of septa. All the tentacles are covered with round batteries of nematocysts 

 which are largest at the tips. The retractor muscles of the mesenteries are ar- 

 ranged as in Hexactiniae. The fibres of the tertiary mesenteries arise only from the 

 tentacles while those of the primary and secondary arise from the whole of the 

 mouth disc. There is a circular sphincter (Rotteken's) muscle in the disc. Only 

 the primary and secondary mesenteries are attached to the stomodaeum. The me- 

 senterial filaments are attached to the mesentery along their whole length and are 

 without acontia, the filaments of the primary and secondary mesenteries are direct 

 continuations of the lower edge of the stomodaeum. The central part of each fila- 

 ment is crowded with goblet vacuoles and corresponds to the "Drlisenstreif", the 

 lateral lobes being homologous with the "Flimmerstreifen" of the Hertwigs. Ne- 

 matocysts are numerous in the convoluted part of the filament and there are no 

 goblet cells here. The filaments of the tertiary mesenteries are similar but smaller. 

 There are mucous and granular gland-cells in the ectoderm of the polyps. Beneath 

 the ectoderm of the oral disc there is a finely punctate layer of nerve fibrils. Mu- 

 cous gland cells are numerous near the mouth of the stomodaeum. Beneath each 

 battery of nematocysts on the tentacles there is an enlargement of the nervous 

 layer. When the thread is extruded the whole nematocyst is thrown out. In place 

 of this there appears a homogeneous mass of protoplasm extending almost from the 

 level of the surface of the ectoderm to the mesogloeal lamina and having near its 

 base a nucleus. The central part of the mass acquires a definite membrane and 

 subsequently forms a nematocyst. The protoplasm of this part becomes very gra- 

 nular, the granules arrange themselves in spiral lines and fuse together to form 

 the thread. Among the cells lining the stomodaeum there are goblet-like vacuoles 

 swollen with secretion. There is no trace of gonidial grooves. Gonads may be 

 present in the mesoglrea of any of the mesenteries. Since in longitudinal section 

 through the mesenterial filaments and stomodaeum it is impossible to find any line 

 of demarcation between them , the whole filament of the primary and secondary 

 (and probably also of the tertiary) mesenteries is ectodermic in origin. 



Sardeson states that the one species of Streptelasma (profundum, Owen, corni- 

 culum, Hall.) when fully investigated shows all the characters which have been 

 regarded as distinctive of the other 14 supposed species of this genus, and there 

 remains no good reason for assuming that more than one species is represented 



