138 HIPPOSPONGIA. 



are scattered throughout the cell in an irregular manner, but still they show a 

 tendency to arrange themselves in transverse rows or discs. In this way the 

 cells of the muscular membrane of our sponge may be regarded as a tran- 

 sition form between the simple undifferentiated contractile elements of sponges 

 and the sti'iated muscular cells of higher Ccelentera. This membrane is 

 perforated at the base by the exhalant canals, which lead from the more dense, 

 skeletons portion of the sponge into the askeletous lacunae. 



This muscular membrane above described is thickened at its distal margin. 

 In transverse sections through this distal thickening we find that no spindle- 

 shaped cells take part in its formation, but that it is composed of a highly 

 colourable granular mass, in which large nuclei are abundant. The latter 

 are spherical and measure 0*002 millim. in diameter. From the sides of this 

 structure granular threads extend in a tangential direction, and from its 

 distal surface slender, straight or curved spindle-shaped cells arise. The 

 distal parts of these reach the outer surface. The cells are curved in such a 

 manner that the end is nearly perpendicular to the surface. These cells are 

 0-02 millim. long; at the ends 0-0005 millim. and in the middle 0-0015 

 millim. thick. They are filled with granular protoplasm, which imbibes 

 staining fluids very readily and is turned dark brown by the action of osmic 

 acid. In the central swelling an oval nucleus, 0-002 millim. long and 0-0006 

 millim. broad, is situated. I am of opinion that this structure should be con- 

 sidered an oi'gan of sense, comparable to the ring-nerve of the craspedote 

 Medusae or the sensitive and ganglion-cells which form a circular zone in the 

 entoderm of the manubrium of certain hydroid polyps. The distal thickening 

 of the membrane consists of ganglion-cells the nuclei of which are apparent, 

 the limits of which, however, remain indistinct. The spindle-shaped cells in 

 the skin should be regarded as sensitive elements and their basal processes 

 as nerves, which lead from the sensitive to the ganglion-cells below. The 

 tangential granular threads represent tangential nerves, which lead from the 

 ring-nerve to other parts of the surface. 



Hippospongia canaliculata, var. dura, Lendenfeld. 



Eusjjongia canaliculata, var. dura, E. v. Lendenfeld, " A Monograph of the 

 Australian Sponges. — Part VI. The Genus Euspongia," Proceedings of 

 the Linnean Society of New South Wales, vol. x. p. 502 (1885). 



The main fibres are in this variety slightly and gracefully curved, 0-1 millim. 

 thick and on an average 1-3 millim. apart ; they taper towards the distal end, 

 which supports the dermal sand-cortex. They are entirely filled with small 

 foreign bodies, chiefly sand-grains. The connecting-fibres are clearly distin- 

 guished into primary tangential and secondary radial fibres. The former are 



