98 THE VOYAGE OF H.M.S. CHALLENGER. 



The large sabre-shaped or lateral thread-cells (Cnidocysts ensiformes, kg) form 

 constantly two small lateral groups in the basal or proximal part of the sacculus, covering 

 both the right and left sides of the base, of the cnido-battery. Their number and 

 form are often characteristic of the individual species of Calyconectae. Thus, for 

 example, Mitrophyes peltifera (PL XXVIII. fig. 8) has only two, Oymbonectes huxleyi 

 (PI. XXVII. fig. 7) three, Diphyopsis compressa (PI. XXXIV. fig. 18) six large lateral 

 thread-cells on each side of the base of the sac ; their number is larger in the Abylidae 

 (usually eight to twelve), and especially in the Prayidae (sixteen to twenty, or more, on 

 each side). Their form is usually slender, spindle-shaped or sabre-shaped, four to eight 

 times as long as broad, straight, sometimes slightly curved ; but sometimes they are 

 more rounded, ovate (as in the smallest Calyconectse). They are always placed in a 

 single longitudinal row, parallel to one another, and also (more or less) to the axis of the 

 sacculus. Usually the axis of the ensiform cnidocysts is so directed obliquely that the 

 dorsal end is more proximal and medial, the ventral end more distal and lateral. 



The small pear-shaped or distal thread- cells (Cnidocystse pyriformes, hp) always 

 form an odd group at the distal end of the cnidosac and touch the base of the terminal 

 filament (tf). Their number is very variable, usually between twenty and sixty. The 

 group formed by these pyriform cnidocysts has usually the form of a rounded cap, 

 covering the distal end of the cnido-battery, and is evidently sensitive to a remarkable 

 degree, since long cnidocils arise from these thread-cells. Sometimes the group is tri- 

 lobate, with an odd middle and two lateral lobes ; and in some species it is even divided 

 into three separate parts, an odd medial group being separated from two paired lateral 

 groups, as in Praya (PI. XXXII. figs. 12-14) and in Bassia (PI. XXXVIII. fig. 16). 



The elastic angle-band, composed of two very long linear and parallel ribbands, is 

 closely coiled up spirally in the thin-walled ventral pouch of the closed cnidosac. But 

 when this becomes opened (by rupture of the thin ventral wall), then the angle-band is 

 expanded to a great length, often folded in a zigzag. Its proximal end remains in 

 connection with the pedicle (tp), its distal end with the terminal filament (tf). The 

 cnido-battery becomes hung out, and is freely prominent, and its distal end only re- 

 maining in connection with the proximal part of the terminal filament and its junction 

 with the elastic angle-band (PI. XL. fig. 20). 



Gonophores. — The sexual persons of the Calyconectse are always quadriradial Medusae, 

 with a well-developed umbrella and a manubrium, in the thickened wall of which the 

 sexual cells are produced from the exoderm. The cavity of the manubrium has, 

 however, no mouth opening, and the margin of the umbrella bears no tentacles. 

 Originally each cormidium possesses only one gonophore, and in many Calyconectse 

 never more than a single sexual medusome is attached to the siphon. But when this 

 gonophore is mature, it usually detaches itself from the cormidium (Eudoxia) and may 

 be replaced by a secondary or vicarious gonophore. In many species (mainly of Abylidae) 



