REPORT ON THE SIPHONOPHOR^E. 3 



attribute to the several (morphological) organs of these persons the same individual 

 value {e.g., to the single protective bracts and capturing filaments); is furthermore 

 wrong in denying an extensive secondary multiplication and dislocation of these 

 organs ; and finally is especially at fault in regarding the primary medusoid larva as a 

 merely henogenetic embryonic form, and, by ignoring the palinge'netic value of the 

 latter, in interpreting the Siphonophorae as " swimming Hydropolyp colonies " comparable 

 to Hydractinia. 



MEDUSOME THEORY. 



The new theory of the. organisation of Siphonophoros to which I have been led by 

 my investigations on their comparative anatomy and ontogeny may be briefly designated 

 as the Medusome Theory. It seeks to incorporate the elements of truth in the two 

 views above described, but to avoid their errors. The principal positions of this 

 restatement may be briefly resumed: — 



1. The primary larva, which arises directly from the gastrula of the Siphonophorae, 

 is always a simple Medusa ; it may be more or less kenogenetically modified, but 

 always retains a predominant palingenetic import, and is explained by the immediate 

 derivation of the Siphonophorae from Hydromedusae. 



2. The primary medusiform larva of the Siphonophorse appears in two essentially 

 distinct forms, as a Disconula and a Siphomda, and since this distinction is associated 

 with essential differences in the resulting Siphonophoral colonies, the class may be 

 legitimately divided into two legions or subclasses, — Disconanthae and Siphonanthae. 



3. The first legion, or Disconanthae, including the single order Chondrophoridae or 

 Porpitariae, develops from a regular and octoradial Medusoid larva {Disconula), retains 

 the original corona of marginal tentacles throughout life, and produces the persons of 

 the colony by annular budding from the subumbrella. 



4. The second legion, or Siphonanthae, on the other hand, includes all the other 

 Siphonophorse (Calycophoridas, Physophoridaa, Pneumatophoridae, Aurophoridae) ; its 

 primary larva is a bilateral Medusa {Sii^honula), which is distinguished by a ventral 

 umbrellar cleft and by the possession of a single tentacle ; it forms the persons of the 

 colony by one-sided linear budding from the stomach-wall or manubrium. 



5. The primary larva of the Disconanthse {Disconula) is to be regarded as the 

 ontogenetic recapitulation of a common primitive octoradial ancestor (Archimeda), and 

 its phylogenetic origin is probably to be sought among the Trachomedusae (Trachy- 

 nemidae, Pectyllidee). 



6. The primary larva of the Siphonanthas {Siphomda) is to be regarded as the 

 ontogenetic recapitulation of a common primitive bilateral ancestor {Protomecla), and 

 its origin is probably to be sought among the Anthomedusre (Codonidae, Euphysidae). 



