TETRAXONIDA. 7 



generally, however, it is of smaller size than the body, especially in large and 

 old specimens. 



The porocalyces. In adult specimens the porocalyces form a broad belt round 

 the sides of the body. A few, in large specimens, were nearly 2 '5 cm. (one inch) in 

 depth. As I have already stated (10. p. 662) the porocalyces are, in all species of 

 Cinachjra, inhalant areas perforated by true dermal pores, and are never exhalant or 

 oscular. 



The OSCules. In Cinachyra harbata these structures are arranged in an obscurely 

 spiral manner on the upper or " polar " surface of the sponge in adult .specimens. In 

 almost every instance, the oscules are tightly contracted, the spicular fringe being 

 closed over them in form of a conical stack. It is this strong contractibility that has 

 led to their being overlooked in most of the species of this genus, the porocalyces 

 having been regarded as partly inhalant and partly exhalant. 



The oscules are very rarely found open. Where this happens, the oscular orifice 

 is at the summit of a .slight crater-like elevation. Within the circle of long protriaenes 

 forming the oscular fringe is a circle of fine protriaenes on the edge itself and also 

 on the gentle slope leading inwards. At a .short distance from the edge, the slope 

 leads to a vertical barrel-shaped tube ending in a well-marked sphinctrate ring, which 

 is about on a level with the innermost plane of the cortex ; the oscular tube slightly 

 expands below the sphincter into a sub-cortical cavity in the lateral walls of which are 

 the orifices of exhalant canals proceeding from just beneath the cortex. At its lower 

 end the sub-cortical space is continued on into a large main vertical canal, which passes 

 up radially from the central region, receiving in its turn many affluents. The wall of 

 the oscular tul)e is mainly composed of a thick sheath of concentrically arranged 

 myocytes. 



The vertical section of the oscular tube, when contracted, shows the almost closed 

 lumen of the tube surrounded by a dark zone of sigmata, and with spiral bands of 

 myocytes passing upwards around the lumen. 



Two of the eight known Cinachyra species, viz., C. voeltzkowi Lendenfeld (11. p. 

 101) and C. vialaccensis I. J. B. Sollas (19. p. 219), are described as having .scattered 

 pores in addition to the pores of the porocalyces. Some of these " pores " will certainly 

 be found to be oscules situated, in young specimens, more or less antipodally to the 

 porocalyces, others possilily belonging to developing porocalyces ; for as W. J. Sollas 

 observes (21. p. 29), " in their inception, the porocalyces are simply poriferous areas of 

 the cortex." 



Young specimens. Very young .specimens (IX. 3) are oval, broader at the 

 superior end, and without a root-tuft, though the surface spicules are longer at the 

 narrow end of the sponge. At this stage the sponge lies with its long axis oblique or 

 horizontal. Tlie smallest specimen in this collection is ,3x4 mm. in diameter. It 

 has one porocalyx situated in the centre of one side, and one oscule a little to one side 

 of the centre of the summit of the broad end. This nearly bilateral symmetry calls lo 



VOL. IV. 2 13 



