8 THE SUB-JvINaDOM C(ELENTERATA. 



Nevertheless, the homogeneity of the primi- 

 tively simple sarcode is liable to become diver- 

 sified by the two processes known as 'vacuolation' 

 and * fibrillation.' By vacuolation, clear spaces 

 and granules arise in its substance, of which ex- 

 a,mples are furnished by Actinoplivys and the 

 Gregarince ; by fibrillation, the same tissue may 

 dispose itself in definite lines, as in the so-called 

 stem muscle of Vorticella, and perhaps also the 

 cortical investment of Tethya. Other structures, 

 still further differentiated, are also seen to occur, 

 as the nucleus, pigment-masses, reproductive ele- 

 ments, and the various kinds of cellseform bodies. 

 But no true nervous or muscular tissues are pro- 

 duced, although these creatures manifest, in an 

 humble manner it is true, some amount of con- 

 tractility and sensibility. 



An attempt miglit even be made to arrange 

 the several forms of Protozoa in an artificial 

 ascending series, the successive steps of which 

 Avould ditfer in the relative degree of distinctness 

 between the body-substance proper, and the outer 

 portion, or conventional integument, to which it 

 may give rise. In the lowest members of the 

 group, as Dujardin has remarked, this external 

 investment resembles nothing so much as the film 

 which forms on the surface of flour paste when 

 left to cool. Here pseudopodia are readily 

 emitted from all parts of the body ; but in Paim- 

 phagus, which, like Amoeba, is naked, they are 

 protrusible from one extremity only, the general 

 surface of the body acting, as it were, the part of 

 a more consistent membrane. PVom Pamphagus 

 to Difflugia, and thence to the higher Rhizopoda, 

 in which the outlying portions of the sarcode 



