The present edition has been submitted to thorough revision, and it is hoped that the most important facts which have been brought to light since the appearance of the last edition will be found to be incorporated in it. No very important changes in classification have been introduced, save that the Echinodermata, in accordance with the views of many distinguished naturalists, have been raised to the rank of a sub-kingdom. This alteration necessitates the abandonment of the Annuloida, as a sub-kingdom, and the reference of the Scolecida to the Annulosa ; and though this arrangement is far from being wholly satisfactory, it would seem to be the best that can, under the circumstances and with our present knowledge, be adopted.

Lastly, a considerable number of additional illustrations have been introduced, by which, it is hoped, the work of the student will be proportionately lightened; and it is to these, chiefly, that any increase of bulk in the present edition is to be ascribed.

United College, St Andrews, May 24, 1880.