REPORT ON THE SIPHON OPHOR^E. 



57 



species ; usually each of the three longitudinal rows bears six to nine branches, often 

 twelve to twenty or more (PI. L. figs. 1-6). 



Ontogeny. — The individual development of the Porpitidae has hitherto been unknown. 

 I conclude, however, from the comparative morphology of the new Porpitidae and Disca- 

 lidae here described, that all members of these two families pass through a larval stage 

 very similar to Discalia. This is subject to a shorter or longer metamorphosis, and passes 

 through a stage siradar to Disconalia. The transition from this to Porpalia, the simplest 

 form of Porpitidae, is easy to conceive. The gonostyles accpuire a mouth, and so the 

 sexual palpons of the former are replaced by the sexual siphons of the latter. 



The medusiform gonophores, which are produced from these gonostyles by budding, 

 have the same form and structure as the well-known Discomitra (afterwards CJirysomitra) 

 larvae of the Velellidae. 1 They become sexually mature in the free medusoid state, after 

 having been detached from the gonophores. The larvae which arise from the fertilised 

 egg have not yet been observed. 



Phylogeny. — The comparative morphology of the Porpitidae and Discalidae admits the 

 phylogenetic hypothesis that the former have arisen from the latter. When Disconalia 

 acquires a terminal mouth on the distal end of each blastostyle, it passes over into 

 Porpalia. 



Synopsis of the Genera of Porpitidae. 



I. Subfamily Porpalid^:. 



Umbrella highly vaulted. Pneumato- \ 

 cyst campanulate, with a radially 

 lobate margin. 



II. Subfamily Porpitellid.e. 



Umbrella flat, slightly vaulted. Pneu- 

 matocyst discoidal, without pro- 

 minent radial marginal lobes. 



' Tentacles arranged in eight radial 

 bunches, the eight primary more promi- 

 nent, ...... 



3. Porpalia. 



Tentacles very numerous, in a circular 

 corona, the eight primary not promi- 

 nent, ...... 



4. Porpema. 



Tentacles arranged in sixteen radial 

 bunches, the eight primary and the 

 eight secondary prominent, 



Tentacles very numerous, in a circular 

 corona, the eight primary not promi- 



nent, 



5. Porpitella. 



6. Porpita. 



Subfamdy 1. Porpalid^;, Haeckel. 



Genus 3. Porpalia* Haeckel, 1888. 

 Porpalia, HkL, System der Siphonophoren, p. 30. 

 Definition. — Porpitidae with a lenticular or subglobular strongly vaulted umbrella, in- 

 cluding a campanulate pneumatocyst with radial marginal lobes. Tentacles numerous, 

 arranged into eight or sixteen prominent radial bunches. 



1 57, pi. x. 



2 Porpalia— Marine ring of a buckle, to'jtii, aX/«. 



(ZOOL. CHALL. EXP. PART LXXVTX 1SS8.) 



Hhhh 8 



