.REPORT ON THE SIPHONOPHOE^E. 127 



two overlapping ventral wings, in Monophyes and Cymbonectes (PI. XXVII.) ; it is a 

 conical or campanulate hydrcecial cavity mMuggiaea and Cymba (PL XLL), a cylindrical 

 canal in Sphseronectes. These closed hydrcecia are secondary cavities, produced by concres- 

 cence of the two parallel ventral wings, which overlap the hydrcecial groove of the former. 



The singular genus Mitrophyes (PI. XXVIII.) is distinguished by the lack of a 

 hydrcecium. It is replaced by an apical scutiform bract, which covers the nectophore 

 and protects the siphosome hidden between them both. The apical bract is probably 

 the remnant of the original primary nectophore. 



Nectosac. — The subumbrella in most Monophyidse occupies the dorsal part of the 

 nectophore, whilst the hydrcecium is placed in its ventral part. The nectosac of 

 Sph&ronectes and Mitrophyes is placed rather basally (as in the ancestral Medusae), in 

 the other genera rather dorsally. The four radial canals are in the former genera rather 

 regularly disposed, but usually more bilaterally, the ventral canal being shorter, and the 

 dorsal longer than the two paired lateral canals. The ring-canal of the margin, which 

 unites them, is placed above the velum. 



Somatocyst. — The acrocyst or somatocyst (" Saftbehalter ") in most Monophyidse is of 

 moderate size, placed in the apical prolongation of the stem ; its cavity is narrow, usually 

 filled by large vacuolate entoderm-cells, and its apex mostly contains an oleocyst. It is 

 directed sometimes vertically upwards, at other times more obliquely. Its structure is 

 the same as in the other Calyconectae (compare above, p. 93). 



Siphosome. — The long tubular stem exhibits in the Monophyidae the same structure 

 as in the Diphyidae. The median ventral line of the common stem is beset at regular 

 intervals by the cormidia, whose number is very variable. The contracted siphosome 

 may be retracted into the hydrcecium more or less completely. 



Cormidia. — Each cormidium (Diphyozooid or Eudoxia) is composed in the Mono- 

 phyidae (as in the most Diphyidae) of two medusomes ; the sterile medusome has a 

 bract, a siphon, and a tentacle ; the fertile medusome is a gonophore, the umbrella of 

 which has the usual medusoid structure, whilst the manubrium produces the sexual cells 

 (compare above, p. 94). 



Siphon and Tentacle exhibit no important differences in the cormidia of the various 

 Monophyidse, whilst the bracts or hydrophyllia are of very different form and structure, 

 characteristic of the genera (compare above, pp. 95, 96). 



Eudoxise. — The cormidia of some Monophyidae arrive at sexual maturity whilst 

 attached to the stem ; they remain sessile eudoxomes. This is the case in Mitrophyes 

 and Cymbonectes, and probably also in Monophyes. The cormidia of the three other 

 genera are detached from the stem, and become mature as free-swimming Eudoxise; 

 those of Sphseronectes are described as Diplophysa; those of Muggiasa as Cucubalus, 

 whilst the free Eudoxiae of Cymba belong to Cuboides. 



Ontogeny. — On the development of the Monophyidae, compare above, pp. 100-102. 



