EEPOPT ON THE SIPHONOPHOE^E. 325 



300 to 400 mm. or more, but when contracted measured only 20 to 30 mm. The long and 

 slender stem is a cylindrical tube scarcely 1 mm. in diameter when contracted, 2 or 3 mm. 

 when expanded. It bears a series of ten to twelve fully developed cormidia in the 

 larger specimen, besides numerous buds of young ones on the top of the stem, below the 

 float. The ordinate cormidia are separated by naked internodes of equal length, the 

 colour of the stem and the gonodendra is bright yellow, of the siphons and tentacles rose. 



Pneumatophore (figs. 1-3, p, fig. 4, in profile; fig. 5 from above). — The large ovate 

 or pyriform float has when contracted a length of 6 mm. and a breadth of 3 mm.; in the 

 expanded state more than double this. Its thick-walled pneumatocodon (or outer wall) 

 is separated by a wide cavity from the pneumatosac (or inner wall) ; this cavity (the 

 pericystic chamber) is closed above and opens below into the axial canal of the- trunk; 

 its greater part is filled up by clustered groups of finger-shaped villi, which arise from 

 the hypocystic funnel (fig. 4, j )V )- The large exodermal giant-cells which compose 

 these villi reach the enormous size of 1*5 to 2 mm.; the surface of the villi is covered 

 with a simple layer of ciliated entoderm cells (fig. 6). The thin chitinous wall of the 

 cuticular pueumatocyst is covered outside by the simple exoderm-layer of the pericystic 

 pneumatosac, inside by the thick yellowish-green endocystic tapetum (fig. 4, pf) ; this is 

 composed of several strata of polyhedral exoderm-cells, filled with greenish granules 

 (fig. 7). The endocystic tapetum is wanting only in the uppermost third or fourth of 

 the pneumatocyst, which is covered outside by a hemispherical or cap-shaped mitra ocellaris 

 (figs. 4, 5, pp). Above this mitra, which is composed of red polygonal pigment-cells, are 

 visible the radial muscles {pin) and the circular muscles of the sphincter {pn), which 

 closes the stigma, or the apical opening of the pneumatocyst (fig. 5, po). (For the 

 special structure of the pneumatophore, compare above, p. 308.) 



Siphons (figs. 1-4, s). — The feeding polypites are large cylindrical tubes of rose-colour, 

 which open outside by the distal mouth, inside by the small proximal pedicle into the 

 trunk. The thick muscular wall is very extensible and contractile, as is also the mouth, 

 which may be expanded in the form of a circular suctorial disc. Distinct segments are not 

 visible on the siphon ; the greater part of its inside is covered with small and very 

 numerous hepatic villi. 



Tentacles (fig. 8). — The large cylindrical and rose-coloured tentacle, which is attached 

 to the base of each siphon on its dorsal side, bears a series of very numerous tentilla ; 

 their size increases gradually towards the distal third of the tentacle ; this third is a 

 simple, thick, cylindrical tube, spirally coiled up, more deeply coloured, and covered with 

 small papillae, but without tentilla. The lateral branches are small and simple in the 

 proximal part of the tentacle, trifid in the middle part. Each fully developed tentillum 

 bears at the distal end an odd thick median club (fig. 9, to) with a short terminal filament 

 {tf) ; and on both sides of it a pair of slender cylindrical lateral horns {tc). Each of 

 these three terminal appendages contains two rose-coloured cnidonodes, composed of 



