REPORT ON THE SIPHONOPHOR^. 19 



BRACTS or COVERING PIECES. 

 (Hydrophyllia, Protecta, Deckblatter, Covering Scales, Phyllozooids). 



The polymorphic organs which are usually spoken of as " covering pieces" 

 (Deckstiicke) are entirely absent in the three orders Disconectae, Cystonectae, and 

 Auronectaa ; in the former originally, in the two latter probably as the result of degenera- 

 tion. In the two remaining orders the bracts are essentially distinguished in this, that 

 in the Calyconectae they appear singly on each Medusome, in the Physonectae on the 

 other hand there are several. Only the primary larva of the latter (Siphonula) frequently 

 forms a single " primary covering piece " (Protobractea), which is then to be compared 

 with the single bract of the former (Eudoxia), and to the umbrella of the primary 

 ancestral form (Protorneda). 



The physiological importance of the bracts consists exclusively in their protective 

 function ; they are shields or umbrellar organs, under the shelter of which the other 

 persons of the colony are protected. As regards their morphological import, the poly- 

 person theory regards them as degenerate medusoid persons, which have lost manubrium 

 and tentacles, while the gelatinous disc has been the more developed; the poly-organ 

 theory, on the other hand, regards them as multiplied umbrellas. According to our 

 medusome theory, a distinction must be drawn between primary and secondary bracts. 

 The protobracteae or primary covering pieces, which occur singly, on the larvae of 

 Physonectae and on the Eudoxiae of Calyconectae, are to be interpreted as the umbrella 

 of a primary medusoid person. The metabracteae or secondary covering pieces, however, 

 which usually cover the stem of the Physonectae in large numbers, may have various 

 phylogenetic origins. They may arise as — 



(1) Displaced umbrellas of secondary medusomes ; 



(2) Vicariae or multiplied reserve-bracts of the same ; 



(3) Cleft portions of divided (e.g., quadripartite) umbrellas. 



The direct transition of nectophores into bracts is to be observed among the 

 Physonectae in the Athoridae and Anthophysidae. In Athoria and Rhodophysa, I find 

 in the distal portion of each bract a small rudimentary nectosac or swimming cavity, 

 sometimes with four cnidonodes or stinging knobs, which may be regarded as the rudi- 

 ments of four reduced tentacles. The highest and most manifold development of bracts 

 is found in the Calyconectae, where the sterile medusome of each single cormidium bears 

 a large hydrophyllium of a peculiar form, often characteristic of the genus. The phyllo- 

 cyst, too, or the canal of the bract, here often exhibits several apophyses, which may be 

 regarded as rudimentary radial canals of the umbrella; e.g., Aglaisma, the free Eudoxia 

 of Calpe, possesses four radial canals in its bract, two paired lateral and two odd sagittal 

 (an ascending and a descending canal). 



