REPORT ON THE SIPHONOPHOR^E. 95 



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

 and Erssea, Families IV. and V.). 



Bractese or Hydrophyllia (Protective persons or shields, Protecta, Pkyllozooids — 

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

 Calyconectae, tke Monopkykke, Diphyidae, and Desmophyidae, possess constantly a single 

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

 kas been lost by reduction. Tke single bract of eack cormidium is tke reduced umbrella 

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

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

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



Eack bract kas a convex exumbrella and a concave subumbrella, both separated 

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

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

 more or less to tke form of tke first nectopkore. It is hemispherical, mitriform or 

 subspherical, with a smooth exumbrella, in the polygastric Spkaeronectidae, Prayidae, 

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

 edged exumbrella, a ventral fissure, and a pointed apex in tke Cynibonectidae and 

 Diphyopsidae ; it is prismatic with polygonal faces and sharp edges in the Abylidae. 



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

 but has lost its important muscle-plate ; it embraees 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 tke same point arises also tke pkyllocyst, 



Pliyllocyst. — Tke apical cavity or corypkal cavity of tke bract, which we call shortly 

 " pkyllocyst," corresponds to tke acrocyst or somatocyst of tke nectopkore. Its form and 

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

 genera of Calyconectae. Usually tke pkyllocyst is an ovate or spindle-skaped sacculus of 

 tke same structure as tke acrocyst, filled witk 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 subumbrellar cavity, and projects into the thick 

 jelly- substance of tke bract. From its base arise sometimes four radial canals, wkick 

 correspond to tke four original subumbrellar radial canals of tke nectopkorcs, in Praya 

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

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

 tke sagittal plane (dorsal and ventral). Tke majority of tke Calyconectae do not now 

 possess tke four original canals. Cyniba and Abyla have only two lateral canals; 

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

 entirely lost (Diphyes, Monophyes. &c). 



