20 OF THE RHIZOPODA IN GENERAL :—RADIOLARIA. 



many as sixteen. Whilst the digestive process, which usually occupies some hours, is going 

 on, a sort of slow circulation takes place in the entire mass of the endosarc, with its in- 

 cluded vacuoles. If, as often happens, the body taken-in as food possesses some hard 

 indigestible portion (as the shell of an Entomostracan, or the lorica of a Rotifer), this, 

 after the digestion of the soft parts, is gradually pushed towards the surface, and at last 

 escapes by an anal opening in the ectosarc, which extemporises itself for the occasion. 

 Sometimes it may be seen to glide along a pseudopodiiim from its base towards its apex, 

 after the manner of an animalcule captured as food, but in a reverse direction. 



« 



15. When an Adbiophri/s is carefully observed for some little time, a rounded promi- 

 nence is seen to rise slowly and gradually from a particular point on its surface (fig. 1, a), 

 sometimes increasing until it attains in small individuals nearly one-third of the bulk of the 

 entire body, but generally stopping at about one-eighth or one-tenth. The substance of this 

 prominence is so extremely pellucid that it looks almost like a soap-bubble ; and its margin 

 is so well defined as to be more clearly distinguishable than that of the body generally. 

 When it has attained its full size, it suddenly contracts and disappears entirely, so that a 

 flattening of the outline is often observable at the point previously occupied by this remarkable 

 elevation ; the margin soon becomes rounded 'again, and gradually rises anew into a projec- 

 tion, which attains its previous highest development, and then suddenly disappears as before. 

 This alternation of quick contraction and slow dilatation, which maybe seen to go on with 

 great regularity for many hours continuously, obviously marks this body to be a "contractile 

 vesicle," analogous to that of Infusoria ; and it is probable that (as may be clearly made out 

 in certain forms of that group) the fluid propelled by its contractions is transmitted through 

 channels in the protoplasma, some of which it distends into " vacuoles," whose contents^ 

 by a slow contraction of the substance in which they are excavated, are subsequently 

 propelled back into the contractile vesicle. Sometimes the " vacuoles " approach the surface 

 very closely, and may even form projections from it, so that they have been supposed to be 

 multiple contractile vesicles. The true contractile vesicle, however, is distinguished by the 

 constancy of its position, by its sharper outline, and by the rhythmical regularity of its alter- 

 nating contractions and dilatations. 



16. Of the reproduction of Adinophrys so little is at present certainly known, that it will 

 be preferable to bring the observations which have been made upon it into connection with the 

 similarly incomplete fragments of this portion of their life-history, which have been attained 

 by the study of other types of Rhizopod structure (1^ 41, 43). 



17. The several genera that rank with Adinnplnys in the family Actinophryna present 

 its fundamental type of structure under various special modifications. Tiius in Tridiodiscus 

 the body has the form of a flattened spheroid, and the pseudopodia do not radiate from all 

 parts of its surface, but form a sort of zone round its equatorial region only. In PlayiopUrys, 

 again, the origin of the pseudopodia is still more limited, for they all pass off in a bundle from 

 one and the same part of the body ; and this restriction seems to be related to the investment 

 of the body at other parts by a definite limiting membrane, which is still, however, very 

 flexible. In P. cylindrica (Plate I, fig. 6), the body is elongated in form, and the pseudopodia issue 



