22 



PROTOZOA 



Fia. XVI. Radiolaria, 1. Lithocircus annularis, Hertwig ; one of the 

 Monopylica. Whole animal in the living state (optical section), a, nucleus ; 

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

 central capsule (Monopyliea). 2. Cystidiuiu incniie, Hertwig ; one of the 

 Monopyltea. Living animal. An example of a Monopylaeon destitute of 

 skeleton, fl, nucleus ; 6, capsule-wall ; c, yellow cells in the extraeapsular 

 protoplasm. 3. Carjincaniuni diadema, Haeck. ; optical section of the bee- 

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

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

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

 gracillimum, Haeck. ; living animal, complete ; one of the Tripylrca. a, the 

 characteristic dark pigment (pheeodmm) surrounding the central capsule ft. 

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

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

 Tripytea, isolated, showing a, the nucleus ; b,c, the inner and the outer 

 lamina? of the capsule-wall ; d, the chief or polar aperture ; c,c, the two 

 secondary apertures. 6, 7. Acanthmmt rn Claimredei, 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 niultinnclear condition by the 

 breaking up of tile large nucleus, a, small nuclei ; ft, large fragments of 

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

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

 spkirra streptacantlia, Haeck. ; one of the Peripylrca. .Siliceous skeleton 

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

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

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

 Aulosphxra eUgantousiTMt, Haeck.; one of the 1'hajodaria . Half 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 (phieodium 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. 



Fam. 1. PH^EOCYSTIDA, Haeck. The siliceous skeleton is either 

 entirely absent or consists of hollow needles which are disposed 

 outside the central capsule, regularly or irregularly. 



Genera (selected). Aulacantha, Haeck. ; Thalassoplancta, Haeck. 



Fam. 2. PH^EOGROMIDA, Haeck. The siliceous skeleton consists 

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

 dipk'uric, but always has one or more large openings. 



Genera (selected). Challcngeria, Wy. Thomson; Litliogromia, 

 Haeck. 



Fam. 3. PHOSPH.ERIDA. The siliceous skeleton consists of 

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

 a large spherical or polyhedral basket-work. 



Genera (selected). Aulosplmra, Haeck. (Fig. XVI. 9); Aulo- 

 plegma, Haeck. ; C'annacantha, Haeck. 



Fam. 4. PH^OCONOHIDA. 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). Gonchidimn, Haeck. ; Ccelodcndrum, Haeck. 

 (Fig. XVI. 4). 



SUB-CLASS II. Acanthometridea, Lankester ( = AcantUno-skeUta). 



Characters. Radiolaria in which the skeleton is composed of a 

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

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

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

 wall 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. Karely 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 ; nevei' 

 forming a fenestrated shell. 



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

 Astrolonclie, Haeck. ; AmpJiilonche, Haeck. (Fig. XIV. 18). 



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



Genus unieum. Diploeonus, Haeck. 



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

 the skeleton form by transverse outgrowths a spherical fenestrated 

 shell. 



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



Fam. 4. SPHJEROCAPSIDA, Haeek. The twenty acanthin spines 

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

 of acanthin. 



Genus unieum. Sph&rocapsa. 



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

 radiating from a single point without definite number or order. 



Genera. Litholuphus, Haeck. ; Astrolophus, Haeck. 



Further remarks mi the Radiolaria. 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 

 differences 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 Acanthomctrid skeleton, it seems 

 proper to separate them altogether from the other Radiolaria. The 

 PeripyLea 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 Monopyliea and Phajodaria which have modified the capsule 

 but retained the siliceous skeleton. 



Phffiodaria. 



PcripyUea. 



Monopytea. 



Acanthometridea. 



Archi-peripyliea. 

 RADIOLARIA. 



The occasional total absence of any siliceous or acanthiuous 

 skeleton docs not appear to be a matter of classiticatory importance, 

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



