MORPHOLOGY AND RELATIONS OF SIPHONOPHORA 21 



of diphyine Diphyidae, but we know little of the ontogeny of any species of the Diphyidae Tribus- 

 Intermedia of Moser, or of the Abylidae. 



Text-fig. i. Phylogeny of Abylids. Anterior nectophores (in position for horizontal progression) arranged in sequence to 

 suggest evolutionary trend. Fig. 1 H will be seen, on comparison with Text-fig. 2, to resemble larval forms. A, Chuniphyes 

 multidentata ; the tooth T and ridge XT are missing in subsequent forms ; B, Ceratocymba sagittata ; C, Ceratocymba leuckartii; 

 D, Ceratocymba dentata; E, Abyla trigona; F, Abyla haeckeli; G, Abylopsis tetragona; H, Bassia bassensis. Ridges XY and 

 ab respectively are homologous. Ridge ab l is an extension of ridge ab. Ridge XA in C, E and F is homologous. 



B 



Text-fig. 2. A, The larval 'calyconula' (Muggiaea atlantica, after F. S. Russell) representative of many Calyconects, compared 

 with B, Sphaeronectes sp., and C, the anterior nectophore of Bassia bassensis. N, larval nectophore; N 2 , first definitive necto- 

 phore; S, somatocyst, G, gastrozooid. 



In tentatively reconstructing a phylogenetic sequence of forms, and in crudely using present-day 

 forms as some sort of guide, it is often difficult to decide in which direction evolution has proceeded. 

 So, for instance, the present-day species of the last two groups mentioned above may be arranged pro- 

 visionally as a sequence, which suggests that evolution either started or ended with a Bassia-like form, 



