{ { {17a. Phæodinida. { {17. Phæocystina, {17b. Cannorrhaphida. { { {17c. Aulacanthida. {VII. PHÆOCYSTINA { IV. Legion { (Phæodaria { {18a. Orosphærida. (or Subclass){ palliata) {18. Phæosphæria, {18b. Aulosphærida. Phæodaria { { {18c. Cannosphærida. (CANNOPYLEA).{ { { {19a. Challengerida. [Osculosa { {19. Phæogromia, {19b. Castanellida. cannopylea.]{VIII. PHÆOCOSCINA { {19c. Circoporida. { (Phæodaria { { loricata) { {20a. Concharida. { {20. Phæoconchia, {20b. Coelodendrida. { { {20c. Coelographida. 156. _Formation of Species._--The totality of similar forms, which we unite in one species, and which in the earlier dogmatic systems was regarded as a category of absolute value, possesses only a _relative value_ like all other systematic categories (§ 155). According to the individual views of the systematist and the general survey which he has attained of the smaller and larger systematic groups, the conception of a species adopted in his practical work will be wider or narrower. In the present systematic arrangement a medium extent has been adopted. It is shown that in the Radiolaria, as in all other extensive groups of organisms, the constancy of the species is very variable in the different groups. Many families of Radiolaria are very rich in "bad species," _i.e._, very _variable_ forms, in which the process of the formation of species is seen in progress; such, for example, are--among the SPUMELLARIA, the Sphærozoida, Stylosphærida, Phacodiscida and Pylonida; among the ACANTHARIA, the Amphilonchida and Phractopeltida; among the NASSELLARIA, the #Stephoidea# and #Botryodea#; and among the PHÆODARIA, the Aulacanthida, Sagosphærida, Castanellida and Concharida. On the {civ}other hand, in some families numerous "good species" may be distinguished, since the intermediate connecting forms are no longer present and the forms have become _relatively constant_. As instances of such families may be mentioned, among the SPUMELLARIA, the Astrosphærida, Cyphinida, Porodiscida and Tholonida; among the ACANTHARIA the Quadrilonchida and Dorataspida; among the NASSELLARIA, the #Spyroidea# and #Cyrtoidea#; among the PHÆODARIA, the Challengerida, Medusettida, Circoporida and Coelographida. The more carefully the different groups are studied, the more numerous the individuals of each species under comparison, the greater becomes the number of "bad" species among the Radiolaria, and the smaller the number of good ones. Originally, no doubt,