In addition to the treasures of the Challenger, my own collection of Radiolaria has yielded many new forms whose description is here included. On my journeys to the Mediterranean (an account of which is given in the introduction to my Monograph of the Medusæ), I have given special attention to these delicate microscopic organisms for more than thirty years. Besides the various points on the Mediterranean, the Atlantic Ocean at the Canaries (in the winter of 1866-67) yielded many interesting new forms; whilst my voyage across the Indian Ocean, from Aden to Bombay, in November 1881, thence to Ceylon and back by Socotra in March 1882, was still more productive. In particular, some extended excursions which I had the opportunity of making from Belligemma and Matura (at the southern extremity of Ceylon) gave me an insight into the rich treasures of the Indian Ocean.

Most important, however, as regards the knowledge of the Indian Radiolaria, are the collections which Captain Heinrich Rabbe of Bremen has so beautifully preserved during his many voyages through that region. In the neighbourhood of Madagascar and the Cocos Islands more especially, and also in the Sunda Archipelago, he met with large swarms of Radiolaria, among which were many new and remarkable forms. These were of special value for completing the chorology, and the more so since the course of the Challenger in the Indian Ocean lay very far to the southwards. I will therefore take this opportunity of repeating my best thanks to Captain Rabbe for the friendly donation of his valuable collection.

The Radiolarian fauna of the North Atlantic Ocean, which was previously but little known and only slightly increased by the investigations of the Challenger, received a valuable increase from the interesting collections made by Dr. John Murray on various expeditions to the Færöe Islands (on the "Knight Errant" in 1880 and on the "Triton" in 1882). A large number of new Radiolaria were captured in the Færöe Channel, partly at the surface of the Gulf Stream, partly at various depths, and the proof was thus furnished that at certain points in the North Atlantic Ocean Radiolaria are very richly developed. I am further indebted to Dr. John Murray for the free use of this important material as well as for much other assistance in the carrying out of my work. Another rich source of Radiolaria I found in the alimentary canal of pelagic animals from all seas. Medusæ, Siphonophoræ, Salpæ, Pteropoda, Heteropoda, Crustacea, &c., which live partly at the surface of the sea and partly at various depths, and swallow large masses of Radiolaria, often contain numbers of their shells well-preserved in their intestine. The alimentary canal of Fishes and Cephalopods too, which live upon these pelagic animal frequently contains considerable quantities of siliceous shells; and another newly discovered source has been found in the coprolites of the Jurassic period, which consist largely of Radiolarian skeletons.

In the investigation of this complicated system of organisms, I have endeavoured on the one hand to give accurately the forms and dimensions of the species observed, and on the other hand to present a survey of the relationships of the different genera and families; and in this I have striven especially to combine the phylogenetic aims of the natural system with the essentially artificial divisions of a practical classification. Being, however, a conscientious supporter of the theory of descent, I can of course lay no stress upon the value of the categories, which are here distinguished as Legions, Orders, Families, Genera, &c. All these artificial systematic grades I regard as of merely relative value; and from the same cause I attach no importance to the distinction of all the species here described; many of them are probably only developmental stages, and like my predecessors I have determined their boundaries on subjective grounds. In the systematic working out of so much material one always runs the risk of doing either too much or too little in the way of creating species; but in the light of the theory of descent this danger is of no consequence.

In the carrying out of this extensive task the friendly aid of Dr. Reinhold Teuscher of Jena was of the greatest benefit to me; at my request he was at the trouble of making a large number of accurate drawings with the camera lucida, and he also undertook a long series, amounting to some 8000, accurate micrometric measurements, which were of the greatest value in the attempt to settle the important question of the constancy of the various species; I have alluded to this in a note at the conclusion of the Report (p. [1760]). My best thanks are due to Dr. Teuscher for the patient and careful manner in which he discharged these tedious tasks.

The figures of new species of Radiolaria (about 1600 in number) which appear in the atlas of one hundred and forty plates accompanying this Report, were nearly all drawn with the camera lucida, partly by Mr. Adolph Giltsch and partly by myself. The names of the genera which appear at the bottom of the plates have in many cases been changed since they were printed off, as may be seen from the explanations which accompany them. Had it been possible to complete the examination of the material before the plates were commenced this might have been avoided, and in many cases a better selection of figures might have been made. All the drawings have been made upon the stone by the practised hand of Mr. Adolph Giltsch, in his usual masterly manner, and his lithographic work, which has lasted fully ten years, is the more valuable since he has himself microscopically studied the greater part of the species figured. The fact that the atlas presents so full a picture of the marvellous wealth of form of the Radiolaria is especially due to his lively interest in the work, to his unwearying care, and to his morphological acuteness. May it be the means of inducing many naturalists to study more deeply this inexhaustible kingdom of microscopic life, whose endless variety of wonderful forms justifies the saying—Natura in minimis maxima.

CONTENTS.

FIRST PART.
GENERAL INTRODUCTION—PAGE
I.Anatomical Section (§§ 1-140),[i]
ChapterI.The Unicellular Organism,[i]
"II.The Central Capsule,[xxiv]
"III.The Extracapsulum,[li]
"IV.The Skeleton,[lxviii]
II.Biogenetical Section (§§ 141-200),[xciii]
ChapterV.Ontogeny (Individual Development),[xciii]
"VI.Phylogeny (Genealogical Development),[ci]
III.Physiological Section (§§ 201-225),[cxxviii]
ChapterVII.Vegetative Functions,[cxxviii]
"VIII.Animal Functions,[cxl]
IV.Chorological Section (§§ 226-250),[cxlvi]
ChapterIX.Geographical Distribution,[cxlvi]
"X.Geological Distribution,[clxiv]
V.Bibliographical Section (§§ 251-254),[clxxvi]
SYSTEMATIC PART,[1]
I.Subclass PORULOSA,[6]
Legion I. SPUMELLARIA vel PERIPYLEA,[6]
Order1.Colloidea,[10]
"2.Beloidea,[28]
"3.Sphæroidea,[50]
"4.Prunoidea,[284]
"5.Discoidea,[402]
"6.Larcoidea,[599]
Legion II. ACANTHARIA vel ACTIPYLEA,[716]
Order7.Actinelida,[728]
"8.Acanthonida,[740]
"9.Sphærophracta,[795]
"10.Prunophracta,[859]

SECOND PART.

II.Subclass OSCULOSA,[889]
Legion III. NASSELLARIA vel MONOPYLEA,[889]
Order11.Nassoidea,[895]
"12.Plectoidea,[898]
"13.Stephoidea,[931]
"14.Spyroidea,[1015]
"15.Botryodea,[1103]
"16.Cyrtoidea,[1126]
Legion IV. PHÆODARIA vel CANNOPYLEA,[1521]
Order17.Phæocystina,[1542]
"18.Phæosphæria,[1590]
"19.Phæogromia,[1642]
"20.Phæoconchia,[1710]
Note on the Dimensions and Measurements,[1760]
ADDENDA,[1761]
ERRATA,[1763]
INDEX,[1765]

GENERAL INTRODUCTION.