22 



PROTOZOA 



no. XTI.— Eadiolaria. l- Lithocireus annula/ris, Hertwig ; one of the 

 Monopylsea. 'Wliole animal in the living state (optical section), a, nucleus ; 

 5, wall of the central capsule ; c, yellow cells ; d, perforated area of the 

 central capsule (Monopylsea). 2. CysUdium inerme, Hertwig ; one of the 

 Monopyliea. Living animal. An example of a Monopylieon destitute of 

 skeleton, a, nucleus ; t, capsule-wall ; c, yellow cells in the extracapsular 

 protoplasm. 3. Carpoeaniwm diadema, Haecl^. ; optical section of the bee- 

 hive-shaped shell to show the form and position of the protoplasmic body. 

 a, the tri-lobed nucleus ; 6, the siliceous shell ; c, oil-globules ; d, the per- 

 forate area (pore-plate) of the central capsule. 4. Ccdodemlnbm 

 47raaKtmum,Haeck.;livinganimal, complete; oneoftheTripylaea. a.the 

 characteristic dark pigment (phseodium) surrounding the central capsiile h. 



' The peculiar branched siliceous skeleton, consisting of hollow fibres, and 

 the expanded pseudopodia are seen. 5. Central capsule of one of the 



Tripylfiea, isolated, showing a, the nucleus ; 6,c, tlie inner and the outer 

 laminEe of the capsule-waU ; d, the chief or polar aperture ; e,e, the two 

 secondary apertures. 6, 7. Acanthmnetra Claparedei, Haeck. 7 shows 



the animal in optical section, so as to exhibit the characteristic meeting of 

 the spines at the central point as in all Acanthometridea ; 6 shows the 

 transition from the uninuclear to the multinuolear condition by the 

 hrealring up of the large nucleus, a, small nuclei ; b, large fragments of 

 the single nucleus ; c, wall of the central capsule ; d, extracapsular jelly 

 (not protoplasm) ; e, peculiar intracapsular yellow cells. 8. Spongo- 



' sphiera streptacantha, Haeck. ; one of the Peripylaea. Siliceous skeleton 

 not quite completely drawn on the right side, a, the spherical extra- 

 capsular shell (compare rig. XIV. 17), supporting very large radial spines 

 which are connected by a spongy network of siliceous fibres. 9. 



Auloaphsera elegantissima, Haeck. ; one of the Phaeodana. Hall of the 

 spherical siliceous skeleton. 



capsule has a double membrane and more than one perforate area, 

 viz., one chief "polar aperture," and one, two, or more accessory 

 apertures (Fig. XVI. 5). The nucleus is single. Around the 

 central capsule is an abundant dark brown pigment (ph»odium of 

 Haeckel). The siliceous skeleton exhibits various shapes regular 

 and irregular, but is often remarkable for the fact that it is built 

 up of hollow tubes. 



Tarn. 1. PHiEOCTSTiDA, Baeck. The siliceous skeleton is either 

 entirely absent or consists of hollow needles which are disposed 

 outside the central capsule, regularly or irregularly. 



Genera (selected). — AulacanthajKaeck.; Thalassoplancta, Haeck. 



Fam. 2. PaiEOGEOMiDA, Haeck. The siliceous skeleton consists 

 of a single fenestrated shell, which may be spherical, ovoid, or often 

 dipleuric, but always has one or more large openings. 



Genera {seleotei).^Cha,Uengeria, "Wy. Thomson; Zithogromia, 

 Haeck. 



Fam. 3. PHa;osPH.a;EiDA. The siliceous skeleton consists of 

 numerous hollow tubes which are united in a peculiar way to form 

 a large spherical or polyhedral basket-work. 



Geneva, {s6\ectei).—Aulosphsera, Haeck. (Fig. XVI. 9); Aulo- 

 plegma, Haeck. ; Cannacantha, Haeck. 



Fam. 4. PHiEOCONCHiDA. The siliceous skeleton consists of two 

 separate fenestrated valves, similar to a mussel's shells ; often there 

 are attached to the valves simple or branched hollow tubes of silex. 



Genera (selected). — Conchidium, Haeck. ; Ccelodendrum, Haeck. 

 (Fig. XVI. 4). 



Sub-class II. Acanthometridea, Lankester { = Acanthino-sJceleta). 



Characters. — Radiolaria in which the skeleton is composed of a 

 peculiar horny substance known as acanthin (rarely of silica). 

 The central capsule is uniformly perforate (Peripylaea type). A 

 divided or multiple nucleus is present in the capsule ; the capsule- 

 waU is single. The skeleton always has the form of spines which 

 radiate from a central point within the capsule where they are all 

 fitted to one another. Rarely a fenestrated tangential skeleton is 

 also formed. 



Fam. I. AcANTHONiDA, Haeck. Skeleton consisting of twenty 

 spines of acanthin disposed in five parallel zones of four spines each, 

 meeting one another at the central point of the organism ; never 

 forming a fenestrated shell. 



Genera (selected). — Acanthometra, J. Miiller (Fig. XVI. 6, 7) ; 

 Astrolonche, Haeck. ; Amphilonche, Haeck. (Fig. XIV. 18). 



Fam. 2. Diploconida, Haeck. Skeleton a double cone. 



Genus unicum. — Diploconus, Haeck. 



Fam. 3. Doeataspida, Haeck. The twenty acanthin spines of 

 the skeleton form by transverse outgrowths a spherical fenestrated 

 shell. 



Genera (selected). — Stauraspis, Haeck. ; Dorataspis, Haeck. 



Fam. 4. Sph^rocapsida, Haeck. The twenty acanthin spines 

 are joined together at their free apices by a simple perforate shell 

 of acanthin. 



Genus unicum. — SpTissrocapsa. 



Fam. 5. Litholophida. Skeleton of many needles of acanthin 

 radiating from a single point without definite number or order. 



Genera. — IMholopJius, Haeck. ; Astrolophits, Haeck. 



Further remarks on the Eadiolaria. — It has not been possible in 

 the systematic summary above given to enumerate the immense 

 number of genera which have been distinguished by Haeckel (42) as 

 the result of the study of the skeletons of this group. The important 

 diff'erences in the structure of the central capsule of different Radio- 

 laria were first shown by Hertwig, who also discovered that the spines 

 of the Acanthometridea consist not of silica but of an organic com- 

 pound. In view of this latter fact and of the peculiar numerical 

 and architectural features of the Acanthometrid skeleton, it seems 

 proper to separate them altogether from the other Radiolaria. The 

 Peripylaea may be regarded as the starting point of the Radiolarian 

 pedigree, and have given rise on the one hand to the Acantho- 

 metridea, which retain the archaic structure of the central capsule 

 whilst developing a peculiar skeleton, and on the other hand to 

 the Monopylaea and Phajodaria which have modified the capsule 

 but retained the siliceous skeleton. 



Fhseodaria. 



Peripylaea, 



Monopylaea. 



Acanthometildea. 



Archi-peripyl»a. 

 Eadiolabia, 



The occasional total absence of any siliceous or acanthinous 

 skeleton does not appear to be a matter of classificatory importance, 

 since skeletal elements occur in close allies of those very few forms 



