REPORT ON THE SIPHONOPHORAE. 21 



of the four radial canals of the subumbrella. Only rarely do these portions become 

 more or less rudimentary, so that the medusoid form is lost and passes over into a 

 more or less degenerate " sporosac." The tentacles on the umbrellar margin of the 

 gonophores have usually disappeared ; sometimes, however (as in some Calyconectse), four 

 rudiments are recognisable, and at other times even a corona of tentacular rudiments 

 (Desmojrfiyes). The Disconanthas, in which free reproductive Medusae in the sexually 

 mature state are not yet sufficiently known, may perhaps bud off four or eight separate 

 gonads either from the manubrium, or from the subumbrella. 



As to the distribution of the two kinds of gonophores on the corm, it must be 

 noticed that most of the Siphonophorae are monoecious. Some Calyconectse {Mitroj>hijes, 

 Galeolaria) and some Physonectae (A'polemia, Athoralia) are dioecious. Among the 

 monoecious corms both kinds of sexual persons occur, sometimes in separate cormidia 

 (diclinous), sometimes associated in each single cormidium (monoclinous). The gono- 

 dendra, or the clustered groups of gonophores, are usually distylic, all their branches 

 bearing Medusae of the same sex; male and female gonodendra arising separately. But 

 sometimes there are monostylic gonodendra, the basal part of the single branched 

 gonostyle bearing female, and the distal part male, gonophores (as in the Auronectae 

 and Cystonectas, Forsbdia, &c). On the other hand, hermaphrodite persons {i.e., gono- 

 phores which form both spermatozoa and ova) are not known in this class. The male 

 persons are known as androphores, the female as gynophores. Usually the androphores 

 are slender, more oblong, and bear a spindle-shaped or cylindrical spermarium ; the 

 gynophores are thicker, more rounded, and bear an ovate or ellipsoidal ovarium. 



FUNDAMENTAL FORM (PROMORPH). 



The promorphology of the Siphonophorae has led to .very different views respecting 

 the ideal geometrical fundamental form (or the " promorph "), which may be 

 recognised by abstraction from the concrete single forms of these Acalephs. One group 

 of authors regards the Siphonophorae as " Radiate animals," whilst another group 

 maintains that they are "Bilateral animals." These opposed views are both right in a 

 certain sense. On the one hand, a typical radial structure — generally a quadriradial 

 form, composed of four equal quadrants — is recognisable in all Siphonophorae (mainly in 

 the gonophores and nectophores), and this is in my opinion produced by inheritance from 

 the older ancestral Medusae. On the other hand, a distinct bilateral structure — or a 

 dipieural fundamental form, composed of two symmetrical halves or antimeres — is 

 recognisable in most Siphonophorae, viz., in all Siphonanthae, whilst it is wanting in the 

 Disconanthae. This bilateral type is partly inherited from the bilateral Medusae, which 

 we regard as the ancestors of the Siphonanthae (Protomeda), and the essential form of 



