REPORT ON THE SIPHONOPHOR^. 95 



about under the individual form of self-subsistent monogastric Calyconectse (Eudoxia 

 and Erssea, Families IV. and V.). 



Bractcze or Hydrophyllia (Protective persons or shields, Protecta, Phyllozooids — 

 " Deckstiicke, Deckschuppen " of German authors). — Three families of polygastric 

 Calyconectse, the Monophyiche, Diphyidse, and Desmophyidge, possess constantly a single 

 bract on each cormidium ; it is wanting only in the fourth family, Polyphyidas, where it 

 has been lost by reduction. The single bract of each cormidium is the reduced umbrella 

 of the Medusa-person, the manubrium of which is the single siphon of the former. This 

 is very obvious in Praya, Calpe, and some other genera, where the bract still possesses four 

 radial canals. Usually some of these canals are lost, or they have disappeared altogether. 



Each bract has a convex exumbrella and a concave subumbrella, both separated 

 by the basal margin of the umbrella. The form of the bract is very various, and 

 characteristic of the single genera of monogastric Calyconectas ; usually it corresponds 

 more or less to the form of the first nectophore. It is hemispherical, mitriform or 

 subspherical, with a smooth exumbrella, in the polygastric Sphseronectidge, Prayidse, 

 and Desniophyidse. The bract is pyramidal, spathiform or conical, with sharply 

 edged exumbrella, a ventral fissure, and a pointed apex in the Cymbonectidse and 

 Diphyopsidse ; it is prismatic with polygonal faces and sharp edges in the Abylidse. 



The bracteal cavity corresponds with the suburnbrellar cavity of the ancestral Medusa, 

 but has lost its important muscle-plate ; it embraces the siphon, the single tentacle, and 

 the gonophore ; the last is placed at the ventral side of the siphon, the tentacle at its 

 dorsal side. The nutritive canals of all the organs unite in the top or the centre of the 

 bracteal cavity, where it communicates also with the central canal of the common stem 

 by a short bracteal canal. From the same point arises also the phyllocyst. 



Phyllocyst. — The apical cavity or coryphal cavity of the bract, which we call shortly 

 " phyllocyst," corresponds to the acrocyst or somatocyst of the nectophore. Its form and 

 the number and disposition of its apophyses are often very characteristic of the individual 

 genera of Calyconectae. Usually the phyllocyst is an ovate or spindle-shaped sacculus of 

 the same structure as the acrocyst, filled with large polyhedral vacuolated cells, and 

 often containing also an oleophore or an apical oil-globule. It arises usually more 

 or less vertically from the top of the suburnbrellar cavity, and projects into the thick 

 jelly-substance of the bract. From its base arise sometimes four radial canals, which 

 correspond to the four original suburnbrellar radial canals of the nectophores, in Praya 

 (PI. XXXII. figs. 8, 9) and in Calpe (PL XL. figs. 14-18). These are so arranged that 

 two paired canals lie on both sides of the bilateral bract (right and left), and two odd in 

 the sagittal plane (dorsal and ventral). The majority of the Calyconectae do not now 

 possess the four original canals. Cymba and Abyla have only two lateral canals; 

 Bassia a single basal canal, arising from the base of the phyllocyst ; often they are 

 entirely lost (Diphyes, Monophyes. &c). 



