SECTION I. DISCOSTOMATA-GYMNOZOIDA. 327 



as the Foraminifera, it will moreover be found that, notwithstanding the extreme 

 tenuity of the sarcode film, a circulation of its substance is being constantly 

 maintained, flowing upwards on the outside, over the distal edge or rim, and 

 downwards on the inner surface, at the base of which it again comes in contact 

 and merges with the protoplasmic substance of the body. This wineglass-like film 

 of sarcode doubtless acts as an efficient branchial or respiratory organ, but such by 

 no means represents its most important function. In conjunction with the centrally 

 enclosed flagellum it constitutes a most admirably contrived trap or snare for the 

 capture and retention of the animalcule's food. Whirling round with inconceivable 

 rapidity, the last-named organ, the flagellum, creates a strong centrifugal current in 

 the water, setting in from behind towards the direction of its own apex, and bringing 

 with it all such tiny organic particles as do not possess sufficient weight or power to 

 stem its tide.* But for the outstretched collar, these would simply hurry with the 

 stream past the monad's body and out of reach. Not for them, however, so easy a 

 passing of the rapids ! In the midst of their swift career they strike against the 

 almost impalpable film of sarcode of which the organ is composed, and to this they 

 adhere as tenaciously as a snared bird to a lime-daubed twig or an incautious fly to 

 a spider's web. Then slowly, almost imperceptibly, the captive atoms are carried 

 along with the circulating current of the collar's substance up the outside and down 

 the inside until, on reaching the base of its inner surface, they are engulfed within 

 the sarcode substance of the monad's body. The food-particles after ingestion are 

 gradually accumulated into spherical agglomerations, and then regurgitated through 

 the body under conditions nearly identical with those exhibited by such a higher 

 infusorial type as Vorticella. The indigestible residua are eventually liberated from 

 the area, limited by the base of the collar, within which they primarily gained access." 

 The highly characteristic aspect of an animalcule that has fed upon and become 

 gorged with carmine particles in the manner previously suggested, is delineated in the 

 frontispiece of this treatise, which represents an animalcule of Monosiga gracilis S. K., 

 viewed with the enormous magnification of 8000 diameters, as obtained by a ^V mcn 

 object-glass and C ocular, supplied to the author by Messrs. Powell and Lealand. 

 The arrows placed in various positions serve to indicate the direction of the current 

 induced by the active rotation of the flagellum, and also the course described by 

 the carmine particles after striking upon and becoming adherent to the extended 

 collar. Even where the magnifying power employed is not sufficient to exhibit the 

 cyclosis of the collar substance, the addition of carmine or indigo, in a granular 

 form, to the water containing the animalcules is highly advantageous, since the 

 particles having a tendency to accumulate upon the distal rim of the structure, as 

 shown in the frontispiece, define its contour with an amount of perspicuity 

 obtainable under no ordinary conditions. Most usually, in point of fact, as seen 

 even with adequate magnification, this highly important organ, the collar, is visible 

 only in the optically denser regions represented by the two lateral peripheries, taking 

 the apparent shape then of two linear or setaceous appendages projecting one on 

 either side of the centrally located flagellum. As such apparently simply linear or 

 setose structures, the lateral peripheries of the characteristic collar have indeed been 

 delineated by both earlier and more modern investigators. Examples of monads 

 having their true structure thus only partially revealed, are abundantly furnished by 

 the illustrations reproduced from the authorities referred to, given at Plate II. Figs. 

 12, 16, 19, 20, and 21, PL V. Figs. 32 and 33, and PI. VI. Fig. n. The figure 

 last quoted is of especial interest, since it represents a form included by Mr. Carter 



* This seemingly anomalous direction of the current induced by the motion of the flagellum 

 may be simply and practically illustrated and explained by inserting a stick through a ring and 

 giving them a swift rotatory action, the free or distal end being made to describe the larger circle. 

 Although the stick may be elevated perpendicularly, the ring will travel from the base to its apex, 

 thus demonstrating the centrifugal nature of the force engendered. Such a more abnormal rotatory 

 flagellum will act as a "pu/settum" (see p. 416), driving the body, if detached, backwards through 

 the water. In all ordinary Flagellata the motions of the flagellum are simply undulatory, producing 

 currents in an opposite direction, or towards its base of attachment, and the appendage acting as a 

 " tractellum" drags the body after it, if detached, in a straightforward course. 



