PRIMARY SUBDIVISIONS A UTHOKS S YSTEM. 3 5 



many new species are figured and described in this volume, and also the 

 entire assemblage of the sponges or Porifera. For this group, and with 

 reference to the characteristic discoidal configuration of the introceptive 

 area, the title of the DiSGOSTOMATA, as previously proposed, is still retained. 

 In the third section of the Protozoa, as here defined, the highest degree of 

 organization is arrived at. Here alone, and for the first time, a single 

 simple or often highly differentiated oral aperture or true mouth is met 

 with, for which reason the group appropriately commands the title of the 

 EUSTOMATA. Associated with this section are found the majority of those 

 organisms that collectively constitute the class Infusoria in the more 

 modern acceptation of the term, it embracing the majority of the Ciliata, 

 the Cilio-Flagellata, and such Flagellata as Euglena and Chilomonas, 

 in which the presence of a distinct and circumscribed oral aperture has 

 been clearly demonstrated. With the fourth and remaining natural Pro- 

 tozoic section, the oral or inceptive apparatus exhibits a remarkable and 

 highly characteristic structural modification. This is not, as in the pre- 

 ceding groups, restricted to a definite area, nor is it associated indefinitely 

 with the entire general surface of the creature's body. In place of this, a 

 variable and usually considerable number of flexible retractile tentacle-like 

 organs radiate from diverse irregularly disposed or definite regions of the 

 periphery, each of which subserves as a tubular sucking-mouth, or for the 

 purposes of grasping food. The representatives of this section, including 

 the so-called suctorial animalcules of Claparede and Lachmann, or Tenta- 

 culifera of Professor Huxley, may be literally described as many-mouthed, 

 and appropriately designated the POLYSTOMATA. 



A tabular view of these four sections of the Protozoa as above defined, 

 with their included classes, orders, and characteristic genera, is herewith 

 annexed. Upon examining this table it will be apparent that the 

 secondary subdivisions or classes of the Protozoa, as therein defined, by 

 no means coincide precisely with those more comprehensive and funda- 

 mental sections or groups into which the sub-kingdom may, as just 

 proposed, be primarily divided. Thus, within the section of the Panto- 

 stomata are found comprised the whole of the class Rhizopoda, and a 

 portion only of the Flagellata. The remainder of this last-named class 

 falls partly within the section of the Discostomata, which so far as known 

 includes Flagelliferous Protozoa only, and partly within the more highly 

 differentiated group of the Eustomata ; while within the boundaries of the 

 latter section are included, in addition to the Stomatode Flagellata, the 

 entire class of the Ciliata. It is in point of fact altogether impossible in 

 any such arbitrary and necessarily artificial, lineally arranged table to 

 adequately and intelligibly illustrate the innumerable cross-relationships 

 or lines of evolution that undoubtedly connect these various orders and 

 classes with one another. The special diagrammatic scheme given on the 

 page succeeding that of the tabular view, has therefore been constructed 

 by the writer with the purpose of as far as possible indicating, with the 

 following explanation, the more obvious of these affinities : 



D 2 



