388 
THE VOYAGE OE H.M.S. CHALLENGER. 
swimming — and the changes by which it was produced from the Appendicularia-like 
Proto -Tunicate were probably much the same series of degenerations of certain organs 
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Pig. 11. — Diagram illustrating the phylogeny of the Tunicata. 
and differentiation of others which are found taking place at the present day when the 
free-swimming tailed larva passes into the young Ascidian. The ancestors in which 
these changes took place, and which may be called Proto-Ascidiacea, are represented in 
