The same is true also of the two orders which Ehrenberg distinguished in his class of "Zellenthierchen." The first order is constituted by his "Netzkörbchen" (Monodictya or NASSELLARIA) formerly known as "Polycystina solitaria"; they include our #Cyrtoidea#, the greater part of Hertwig's Monopylea. Ehrenberg's second order is the "Schaumsternchen" (Polydictya or SPUMELLARIA), previously called "Polycystina composita"; they include the Peripylea of Hertwig, as well as the Spyridina (our #Spyroidea#), which belong properly to the NASSELLARIA. Although Ehrenberg's statements regarding the organisation of both these orders were quite erroneous, and his knowledge even of the structure of their shells very defective, I still thought it advisable to retain his names for the groups, since they constituted his one successful effort in the systematic treatment of the Radiolaria (compare L. N. 41, p. 336). The sketch of a systematic arrangement of the Radiolaria (L. N. 37), which I published in 1881 on the basis of the study of the Challenger Radiolaria, resembles, in respect of seven orders being distinguished, the new system which R. Hertwig founded in 1879, in consequence of the variations which he discovered in the structural relations of the central capsule (L. N. 33, p. 133). It differs, however, inasmuch as his Sphærozoea (my Polycyttaria) are here divided into two orders, Symbelaria (#Collosphærida#) and Syncollaria (#Sphærozoida#). In that sketch too I separated for the first time the two subclasses Holotrypasta (Porulosa) and Merotrypasta (Osculosa). The fifteen families established by Hertwig were then raised to twenty-four. The six hundred and thirty genera, which I then distinguished, are still for the most part retained, some, however, in a restricted sense, or with amended definitions. The differential characters of the orders and families of the Radiolaria, given in the Prodromus in 1881, were amended in a further communication which I gave in 1883 regarding the orders of the Radiolaria (L. N. 46, p. 17). There I reduced the seven orders to four, the structural relations of the central capsule being precisely the same in the Polycyttaria and #Collodaria# as in the #Peripylea#. The survey of the affinities of the class was thus rendered much simpler and clearer, and the {clxxxvi}hypothetical genealogical tree, which I then published, has been still further carried out in Chapter VI. of the present Introduction (see §§ 153-200). 253. _General Survey of the Growth of our Systematic Acquaintance with the Radiolaria from 1834 to 1885._ 1834. MEYEN (L. N. 1) describes 2 genera and species of #Collodaria#:--_Sphærozoum fuscum_ and _Physematium atlanticum_. 1838. EHRENBERG (L. N. 2) founds the family Polycystina upon 3 fossil genera (with 6 species):--_Lithocampe_, _Cornutella_, _Haliomma_.