Perhaps the most startling proposition of all those which Professor Haeckel puts before us is that which he bases upon Kowalewsky’s researches into the development of Amphioxus and of the Ascidioida, that the origin of the Vertebrata is to be sought in an Ascidioid form.  Goodsir long ago insisted upon the resemblance between Amphioxus and the Ascidians; but the notion of a genetic connection between the two, and especially the identification of the notochord of the Vertebrate with the axis of the caudal appendage of the larva of the Ascidian, is a novelty which, at first, takes one’s breath away.  I must confess, however, that the more I have pondered over it, the more grounds appear in its favour, though I am not convinced that there is any real parallelism between the mode of development of the ganglion of the Ascidian and that of the Vertebrate cerebro-spinal axis.

The hardly less startling hypothesis that the Echinoderms are coalesced worms, on the other hand, appears to be open to serious objection.  As a matter of anatomy, it does not seem to me to correspond with fact; for there is no worm with a calcareous skeleton, nor any which has a band-like ventral nerve, superficial to which lies an ambulacral vessel.  And, as a question of development, the formation of the radiate Echinoderm within its vermiform larva seems to me to be analogous to the formation of a radiate Medusa upon a Hydrozoic stock.  But a Medusa is surely not the result of the coalescence of as many organisms as it presents morphological segments.

Professor Haeckel adduces the fossil Crossopodia and Phyllodocites as examples of the Annelidan forms, by the coalescence of which the Echinoderms may have been produced; but, even supposing the resemblance of these worms to detached starfish arms to be perfect, it is possible that they may be the extreme term, and not the commencement, of Echinoderm development.  A pentacrinoid Echinoderm, with a complete jointed stalk, is developed within the larva of Antedon.  Is it not possible that the larva of Crossopodia may have developed a vermiform Echinoderm?

With respect to the Phylogeny of the Arthropoda, I find myself disposed to take a somewhat different view from that of Professor Haeckel.  He assumes that the primary stock of the whole group was a crustacean, having that Nauplius form in which Fritz Mueller has shown that so many Crustacea commence their lives.  All the Entomostraca arose by the modification of some one or other of these Naupliform “Archicarida.”  Other Archicarida underwent a further metamorphosis into a Zoaea-form.  From some of these “Zoeopoda” arose all the remaining Malacostracous Crustacea; while, from others, was developed some form analogous to the existing Galeodes, out of which proceeded, by gradual differentiation, all the Myriapoda, Arachnida, and Insecta.