640 PEOFESSOR E. RAY LANKESTER. 



is drawn in fig. 2, PI. XXXIX. The buds have almost the 

 appearance of planula-larvae. Possibly these are young Rhab- 

 dopleur^ developed from eggs and not buds. 



Affinities of Rhabdopleura. 



A knowledge of the development from the egg of Rhabdo- 

 pleura should throw clear light on what is, in reference to this 

 matter, now obscure and uncertain. Some years ago I advocated 

 strongly the view that the buccal-shield or disc of Rhabdopleura 

 and the epistome of the Phylactolsema is the equivalent of the 

 molluscan foot. This view can no longer be maintained if we 

 hold that Rhabdopleura is rightly classed with the Polyzoa, 

 and that Phoronis also is to be classed with them. For Mr. 

 Caldwell has shown that the epistome of Phoronis is the modi- 

 fied prseoral hood of the actinotrocha larva, or at any rate its 

 dorsal portion, and accordingly the epistome of Phylactolsema 

 and the buccal-disc of Rhabdopleura and Cephalodiscus are 

 DORSAL outgrowths. The molluscan foot is ventral, and cor- 

 responds to the body and stalk of a polypide of Rhabdopleura 

 (see my article, '^Polyzoa," in the ^Encyclop. Britannica'), 

 It is exceedingly probable that this is a true orientation of the 

 three types Phoronis, Rhabdopleura, and Phylactolsema. But 

 whilst it is a certainty so far as Phoronis is concerned, since 

 we can identify in the minutest details the surfaces and ciliated 

 areas of the Actinotrocha larva with the surfaces and areas of the 

 trochosphere larva of Mollusca, there is no such certainty with 

 reference either to Rhabdopleura or Phylactolsema ; for of the 

 first we do not know the larva, and of the second, as well as of 

 all other Polyzoa, the larvse appear to be secondary, non- 

 recapitulative forms, which cannot be confidently referred to 

 the trochosphere type, and consequently do not aid us in deter- 

 mining the relations of the regions of the adult to the dorsal, 

 ventral, prseoral, and postoral regions of a trochosphere. 

 Hence we can at present only stumble along in the dark, in so 

 far as Rhabdopleura is concerned. Whatever view is taken of 

 the homology of the buccal-shield, it seems that there can be 



