Professor Haeckel proposes to break up the vertebrate sub-kingdom, first, into the two provinces of _Leptocardia_ and _Pachycardia; Amphioxus_ being in the former, and all other vertebrates in the latter division. The _Pachycardia_ are then divided into _Monorhina_, which contains the Cyclostome fishes, distinguished by their single nasal aperture; and _Amphirhina_, comprising the other _Vertebrata_, which have two nasal apertures. These are further subdivided into _Anamnia (Pisces, Dipneusta, Amphibia)_ and _Amniota (Reptilia, Aves, Mammalia)_. This classification undoubtedly expresses many of the most important facts in vertebrate structure in a clear and compendious way; whether it is the best that can he adopted remains to be seen. With much reason the Lemurs are removed altogether from the _Primates_, under the name of _Prosimiae_. But I am surprised to find the _Sirenia_ left in one group with the _Cetacea_, and the _Plesiosauria_ with the _Ichthyosauria_; the ordinal distinctness of these having, to my mind, been long since fully established. V. In Professor Haeckel's speculations on Phylogeny, or the genealogy of animal forms, there is much that is profoundly interesting, and his suggestions are always supported by sound knowledge and great ingenuity. Whether one agrees or disagrees with him, one feels that he has forced the mind into lines of thought in which it is more profitable to go wrong than to stand still. To put his views into a few words, he conceives that all forms of life originally commenced as _Monera_, or simple particles of protoplasm; and that these _Monera_ originated from not-living matter. Some of the _Monera_ acquired tendencies towards the Protistic, others towards the Vegetal, and others towards the Animal modes of life. The last became animal _Monera_. Some of the animal _Monera_ acquired a nucleus, and became amoeba-like creatures; and, out of certain of these, ciliated infusorium-like animals were developed. These became modified into two stirpes: A, that of the worms; and B, that of the sponges. The latter by progressive modification gave rise to all the _Coelenterata_; the former to all other animals. But A soon broke up into two principal stirpes, of which one, _a_, became the root of the _Annelida, Echinodermata_, and _Arthropoda_, while the other, _b_, gave rise to the _Polyzoa_ and _Ascidioida_, and produced the two remaining stirpes of the _Vertebrata_ and the _Mollusca_.