REPORT ON THE SIPHONOPHORJE. 271 



Bracts (PI. XL figs. 1, 2; PI. XII. figs. 14-16).— The hydrophyllia, or bracts, which 

 make up the main part of the nectosome, form an elegant corona around the pneumato- 

 phore, similar to a double rose, or other flower with numerous petals. Their number is 

 usually between twenty and forty, sometimes more than sixty. They are always thick 

 sickle-shaped scales of a more or less elliptical or lanceolate outline, strongly curved, and 

 attached to the stem by a short pedicle. Sometimes these pedicles are rather broad 

 lamellfe, similar to the pedicles of the nectophores in the Rhodalidae (PI. XII. figs. 7-9, bp). 

 The inner or axial face of the bract is concave and smooth, the outer or abaxial face 

 convex and armed with a variable number of longitudinal ribs or crests, which bear a 

 series of cnidocysts. The thick and firm jelly-substance of the cartilaginous bract 

 encloses a simple canal or phyllocyst, which runs near the inner surface in the median 

 line, and ends blindly at the distal end (fig. 14, be). 



No doubt the bracts of the Anthophysidse are either parts of divided nectophores, or 

 entire reduced nectophores which have lost the nectosac with the subumbrella and the 

 four radial canals, but developed more strongly the jelly-substance of the umbrella, 

 forming a firm protecting scale, or a " cartilaginous shield." The bracts of Rlwdophysa 

 still possess a small rudimentary nectosac at the distal end, similar to that of Athoria, 

 and of the Athorula larvae of many Physonectse (PI. XXL figs. 5-12). The arrange- 

 ment of the bracts in a simple corona, or in several concentric closely apposed circles 

 (one over the other), is very similar to that exhibited by the simple or multiple corona 

 of nectophores in the BhodalidaB (Auronectae). As in these latter, the apparent radial 

 arrangement is at the same time bilateral, since the series of buds in the median 

 ventral line (PI. XII. figs. 7-9, ib) bisects the corona into two symmetrical halves. The 

 corona of bracts in Anthophysa (PL XII. fig. 7, from the dorsal; fig. 8, from the left; 

 fig. 9, from the ventral side) is distinguished by the peculiar bilateral arrangement of 

 the arched ribs of the nectosome, which bear the pedicles of bracts (bj)). Each ridge is 

 composed of four parallel finer ribs ; therefore four bracts are associated in a smaller group. 

 This quadripartite structure may be perhaps explained by the supposition, that each bract 

 is originally the quadrant of a quadripartite umbrella ; the more so as the number of bracts 

 is about four times as great as the number of siphons (the dislocated manubria ?). 



The bracts are organs of protection as well as of locomotion. They cannot change 

 their form ; but they can be elevated and depressed by means of a pedicular muscle, 

 which is attached to their basal pedicle. When freely swimming at the surface of the 

 tranquil sea, the corona of bracts is alternately closed and opened by slowly elevating and 

 depressing the single bracts ; the water protruded from the cavity surrounded by the 

 bracteal corona (and comparable physiologically to the swimming cavity of Medusas) pro- 

 pels the body in the apical direction, the pneumatophore forwards. But when the animal 

 is alarmed the bracts are contracted closely together and surround a subspherical, nearly 

 closed cavity, in which the retracted palpons, siphons, tentacles, and gonodendra are hidden. 



