production of two different kinds of swarm-spores. These two kinds are called isospores and anisospores. The isospores correspond to the ordinary asexual zoospores already described, developing without copulation. The anisospores, on the other hand, are sexually differentiated into female zoospores (gynospores) and male zoospores (androspores). The female, or gynospores, are larger, less numerous, possess larger nuclei, and have a fine filiform network. The male, or androspores, are much smaller, more numerous, with smaller nuclei and thicker tubercles. In some cases both kinds are developed in the same individual, but not always. It is probable that these two forms of anisospores copulate with each other, after their exit from the central capsule, and thus produce a new cell by the simplest method of sexual reproduction. But since the same species which produce these sexual anisospores at other times give rise to the ordinary or asexual zoospores, it is possible that these two forms of reproduction alternate with each other, and that they thus pass through an alternation of generations.

The nutritive materials which these animals require for their support are derived partly from foreign organisms, which they capture and digest (although Dr. Wallich has declared his discredit of this), and partly from the unicellular algæ (Xanthella) which live within them. The considerable amount of starch, and starchy products, elaborated by these tenants (for they are not truly parasites), as well as their protoplasm and nucleus, are available, on their death, for the nutrition of the Radiolaria which harbour them. Nutrition, by means of other particles, obtained by the pseudopodia from the surrounding medium, is by no means excluded; indeed, it is certain that numerous Radiolaria are nourished for the most part, or wholly, by this means. Diatoms, infusoria, as well as decaying particles of animal and vegetable tissues, can be seized directly by the pseudopodia, and conveyed, either to the surface of the jelly-veil, or that of the central capsule, in order to undergo digestion there. The indigestible constituents are collected, often in large numbers, and removed by the streaming of the protoplasm. Professor Haeckel seems to be firm in his opinion on this point, for he alludes to those who have doubted it, and then affirms :- "I must, however, maintain my former opinion, which I have only modified in so much that I now regard the outer surface of the jelly-veil (calymma), rather than the outer surface of the central capsule, as the principal seat of true digestion and assimilation.”

Those bodies called "yellow cells," which at one time were a mystery, and afterwards declared to be statoblasts, are now held to be yellow unicellular algæ, of the group Xanthella, living within the substance of the Radiolaria, and assisting in their support. The animal cells furnish the algæ with shelter and protection, and also with carbon dioxide, and other products of decomposition, for their nutriment, whilst, on the other hand, the vegetable cells of the Xanthellæ yield the Radiolarian its most important supply of nutriment, protoplasm, and starch, as well as oxygen for respiration. It has been experimentally proved that Radiolaria, which contain numerous Xanthella, can exist, without extraneous nutriment, for a long period in closed vessels of filtered sea-water, kept exposed to the sunlight, the two organisms furnishing each other mutually with nourishment. In many Radiolaria the algæ are entirely wanting, therefore they are not absolutely necessary for existence.

Circulation is the general term used to express certain slow currents in the protoplasm, within and without the central capsule, of these organisms. These currents probably continue through the whole life of the animals, and are of great importance for the performance of their vital functions. Sometimes the circulation is directly perceptible in the protoplasm itself, but it is usually only visible owing to the presence of suspended granules. Although the protoplasm of the inner capsule is in communication with that of the outer, through the openings in the capsular membrane, nevertheless the currents exhibit

LATTICE WORKERS, OR POLYCYSTINA. ΙΟΙ

certain differences in the two portions. It is not so easy to observe the movements within the inner capsule as without it, but it is sometimes possible to observe the granules pass through the openings in the capsule membrane. A distinct flowing of the plasma outside the central capsule may be readily observed in all Radiolaria in the living state. This is most easily seen in the free pseudopodia, which radiate from the surface into the surrounding water. In general the direction of the streams is radial, and it is frequently possible to observe two streams, opposite in direction, the granules on one side of the radial thread moving outwards, whilst those on the other side move inwards. If the threads branch, and neighbouring ones become united by connecting threads, the circulation may proceed quite irregularly in the network thus formed. The rapidity of the currents is subject to considerable variation.

In addition to the interior movements of the plasmatic currents, there are also two groups of motor phenomena which may be observed, the contraction of individual parts, which produce modifications of form, and the voluntary or reflex motion of the whole body. Active locomotion, which is perhaps voluntary, occurs in three modes: (1) The vibratile movement of the flagellate swarm-spores, (2) the swimming of the floating organisms, (3) the slow creeping of those which rest accidentally upon the bottom. The movement of the swarm-spores by the oscillation of the thread, or flagellum, does not differ essentially from that of ordinary flagellate infusoria. The swimming of mature Radiolaria is confined to a vertical direction, causing the rising or sinking in the water. This is probably due to increase or diminution of the specific gravity, which is perhaps brought about by the retraction or protrusion of the pseudopodia. The most important organ, however, is probably the jelly-veil, by the contraction of which the specific gravity is increased, while it is diminished by its expansion. The slow creeping locomotion only occurs when the animal comes in contact with a solid surface, and is possibly due to muscle-like contractions of the pseudopodia.

On the subject of phosphorescence in the Radiolaria, Professor Haeckel remarks that "many Radiolarians shine in the dark, and their phosphorescence presents the same phenomena as that of other luminous marine organisms; it is increased by mechanical and chemical irritation, or renewed if already extinguished. The light is sometimes greenish, sometimes yellowish, and appears generally (if not always) to radiate from the fatty sphæres of the inner capsule. Thus these latter unite several functions, inasmuch as they serve, firstly, as reserve stores of nutriment, secondly, as hydrostatic apparatus, and thirdly, as luminous organs for the