THE brief outline of the lower animals given in this account can be augmented by reference to such books as The Royal Natural History (Warne), in several volumes, profusely illustrated but having the disadvantage of being somewhat out-of-date, especially in the matter of classification. A more modern work, by the same publishers, The Standard Natural History, again well illustrated, contains the same information, abridged and brought up-to-date. This has much to recommend it as a work for general reading and, perhaps more particularly, as a work of reference. Articles on special groups will be found in any edition of The Encyclopaedia Britatmica, always worth consulting where an especially full knowledge is
required on a particular subject. For the more academic information concerning classification and anatomy, text-books of Zoology such as those by Parker and Haswell (Macmillan), Shipley and Macbride (Cambridge University Press) and J. Arthur Thomson should be consulted. books dealing with special groups of the lower invertebrates are extremely rare, except for those dealing with the Mollusca, and here no better recommendation can be given than Shell Life by Step (Warne). For the lower marine invertebrates, The Seas, by Russell and Yonge (Warne), is always worth reading, as well as for general accounts of the modern methods of marine investigation.