Transcriber's Note Obvious misprints have been fixed. Archaic and unusual words, spellings and styling have been maintained. Details of the changes are in the Detailed Transcriber's Notes at the end of the book. This book was published in two volumes, of which this is the second. The first volume was released as Project Gutenberg ebook #31558, available at http://www.gutenberg.org/ebooks/31558. Transcriber Added Table of Contents. Page Dedication v Preface vii _Monograph on the Cirripedia_ 1 Introduction 1 On the Names given to the different parts of Cirripedes 3 Class Crustacea, Sub-Class Cirripedia 9 On the Sexual Relation of Cirripedes 23 Order I.--Thoracica 30 Family Balanidæ 33 Table of Contents 33 Structure of Shell 34 Structure of the Individual Compartments 43 Structure of the Radii 45 Structure of the Alæ 47 Structure of the Sheath 48 Structure of the Basis 49 Structure of the Opercular Valves (Scuta and Terga) 51 Growth of the Whole Shell, and Its Microscopical Structure 54 Muscles of Sack 61 Branchiæ 63 Thorax and Body 65 Muscular System 68 Movements and Muscles of the Cirri 71 Mouth 74 Cirri 81 Caudal Appendages 85 Alimentary Canal 85 Circulatory System 87 Nervous System 88 Eyes and Vision 93 Acoustic Organs 95 Olfactory Sacks 97 Male Organs of Generation 97 Female Organs of Generation 100