EEPOET ON THE SIPHONOPHOE^E. 93 



suborder (Cyinbonectarias) would include the Cymbonectidae, Diphyopsidae, Abylidae, 

 and Vogtidae. 



Hydrcecium or Infundibidum (funnel cavity, house-room, Gehiiuskammer, Trichter- 

 hohle, Stamnibehalter). — All polygastric Calyconectae possess a protective cavity, into 

 which the contracted siphosome may retire. This hydroecium (or infundibular cavity) 

 is always an external space, filled with sea-water and invested by the exoderm. In 

 the Monophyidae it is originally an open groove or fossula on the ventral side of the 

 single nectophore (Monophyes, Cymbonectes, PI. XXVII. ). This open groove, or the 

 " hydrcecial sulcus," becomes a closed cylindrical or conical canal, by concrescence of the 

 two opposite margins, or by deeper invagination of the exodermal fossula, in another 

 part of the Monophyidae (Sphwronectes, Muggiaea, Cymba, PI. XLL). The singular 

 genus Mitrophyes (PL XXVIII.) has no hydroecium, but it is replaced here by a pouch- 

 like space between the permanent secondary nectophore and a mitre-shaped or scutiform 

 bract, which is the remnant of the reduced primary nectophore. 



The hydrcecium of the Diphyidse exhibits various degrees of development. In the 

 Prayidae it is an incomplete canal, formed by two opposite ventral grooves of the two 

 nectophores, fitting one into another. Diphyes, Diphyopsis, and the Abylidae possess a 

 conical infundibular cavity at the ventral side of their first or apical nectophore, and this 

 continues into an incomplete hydrcecial canal, formed by a longitudinal groove at the 

 ventral side of the second or basal nectophore. The two margins of this groove are 

 often partly united by concrescence, so as to form a shorter or longer canal. In other 

 cases the two opposite margins of the hydrcecial groove are developed in the form of two 

 broad dentate plates (right and left) which overlap one another. The genus Galeolaria 

 has no hydrcecium, the siphosome hanging freely down between the distal end of the first 

 and the proximal end of the second nectophore. 



The hydrcecium of the Desmophyidae and Poly phy idee is an infundibular cavity 

 between the two opposite rows of nectophores, almost as in the Prayidae. 



Somatocyst or Acrocyst (top-cavity of the stem, coryphal cavity ; Saftsack, Saftbe- 

 halter, cs). — The single nectophore of the Monophyidse, and the first or proximal nectophore 

 of the Diphyidse, contains a remarkable cavity, the acrocyst or somatocyst, at the ventral 

 side of its nectosac and at the top of its hydrcecium. This is the uppermost part of the 

 common trunk included in the jelly-substance of the first nectophore ; it may be com- 

 pared to the apical canal or peduncular canal of the ancestral Medusa, which was con- 

 nected by it with its hydropolyp-parent. The somatocyst is usually spindle-shaped or 

 ovate, at other times subspherical or cylindrical ; its upper or apical end is blind, whilst 

 its lower or basal end passes directly into the small apical central cavity, from which 

 arises the central canal of the stem and the pedicular canal of the nectosac. 



The narrow cavity of the somatocyst, or the acrocyst-canal, is invested by very large 

 entoderm cells, usually vacuolated and polyhedral owing to mutual compression. Its 



