Page:Scientific results HMS Challenger vol 18 part 1.djvu/924

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Acantharia, Haeckel, 1881. Actipylea, Haeckel, 1882. Acanthometrea, Hertwig, 1879. Panacantha, Haeckel, 1878.

Definition.—Radiolaria with simple membrane bounding the central capsule, which is everywhere perforated by innumerable fine pores (disposed either equally or symmetrically). Extracapsulum without phæodium. Skeleton centrogenous (its growth proceeding from the centre), acanthinic (organic, not siliceous). Fundamental form originally spherical.

The legion vel, to the extent here defined, was constituted by me, 1878, in my Protistenreich (p. 102) under the name "." A more accurate definition of this group was given in 1879 by Hertwig under the name. Both names were replaced by me, 1881, in my Prodromus (pp. 421, 465) by the more convenient name. This legion comprises all those Radiolaria which were first described by Johannes Müller, 1858, as Acanthometrae, and also an important part of his Haliomma. In my Monograph (1862, pp. 371-424) I disposed them in three families, Acanthometrida, Diploconida, and Dorataspida.

Although the number of genera and species in this legion is much increased by the rich collection of the Challenger, we can divide all into two different orders:  (without complete lattice-shell) and  (provided with a complete lattice-shell).

The agree with the  in the structure of the simple capsule-membrane, which is perforated by numerous small pores (but constantly devoid of the large main opening, which the  and  possess, being hence united as "Merotrypasta"). We can therefore unite both former legions as "Holotrypasta" (compare above, pp. 5, 6); but in many (if not in all?) the numerous small pores of the capsule-membrane exhibit a certain peculiar arrangement not observed in the ; therefore the latter can be regarded as true "Peripylea" in opposition to the former as "Actipylea."

The peculiar main character of all or  is determined by the chemical constitution of their skeleton, which is not silex, but a peculiar organic substance, called by me in 1862 "acanthin" (Monogr. d. Radiol., pp. 30, 32). In all other Radiolaria the skeleton is composed of silex or of a silicate. But besides this