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 Müller 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_.