104 THE RADIOLARIA 



Amongst the most primitive Radiolaria are the Physematiidae 

 and the allied families Thalassicollidae, Thalassophysidae, etc. In 

 all these forms the hydrostatic jelly is so well developed as to give 

 the term Collodaria to the order formed by them. In the first 

 family, however, the vacuoles elsewhere found in the ectoplasm are 

 endoplastic products, no stratified nutritive concretions are found, 

 and yellow cells are absent. The skeleton, if present, consists 

 merely of scattered spicules. These organisms belong to the 

 surface strata of the ocean and are phosphorescent. Their life- 

 history falls into well-marked nutritive and reproductive phases. 

 The early nutritive stage was erected by Haeckel into a special 

 genus Actissa, which Brandt has shown to be a phase of growth 

 that occurs in at least two of the five families. The later nutritive 

 stage differs in few characters from that of Thalassicolla. The Phy- 

 sematiidae afterwards pass into an isosporous reproductive phase ; 



FIG. 4. 



1, Lithocircus annularis, Hertwig ; one of the Monopylaria. Whole animal in the living 

 state (optical section), a, nucleus ; 6, wall of the central capsule ; c, yellow cells ; d, per- 

 forated area of the central capsule (Monopylaria). 2, Cistidium ine.rme, Hertwig ; one of 

 the Monopylaria. Living animal. An example of a Monopylarion destitute of skeleton, a, 

 nucleus ; b, capsule wall ; c, yellow cells in the extracapsular protoplasm. 3, Carpocanium 

 diadema, Haeck. ; optical section of the beehive-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 

 perforate area (pore-plate) of the central capsule. 4, Coelodendron gracillimum, Haeck. ; living 

 animal, complete ; one of the Tripylaria. a, the characteristic dark pigment (phaeodium) 

 surrounding the central capsule b. The peculiar branched siliceous skeleton, consisting of 

 hollow fibres, and the expanded pseudopodia are seen. 5, central capsule of one of the 

 Tripylaria, isolated, showing a, the nucleus ; 6, c, the inner and the outer laminae of the 

 capsule wall ; d, the chief or polar aperture ; e, e, the two secondary apertures. 6, 7, Acan- 

 thometron 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 Acanthometrida ; a, small 

 nuclei ; b, a parasite (Amoebophrya) ; c, wall of the central capsule ; d, extracapsular jelly ; 

 e, peculiar intracapsular yellow cells. 8, Spongosplinera streptacantha, Haeck. ; one of the 

 Peripylaria. Siliceous skeleton not quite completely drawn on the right side, a, the spherical 

 extracapsular shell (compare Fig. 3 (17)), supporting very large radial spines which are con- 

 nected by a spongy network of siliceous fibres. 9. Aulosplutera degantissima, Haeck. ; one 

 of the Phaeodaria. Half of the spherical siliceous skeleton. (After Lankester.) 



the Thalassicollidae into either isosporous or heterosporous modes 

 of reproduction ; and the Thalassophysidae fragment suddenly into 

 hundreds of minute pieces (see pp. 137-8), without passing, so far as 

 is known, into a sporulating phase. 



In the next division (Sphaerozoa) the polyzoic condition is 

 characteristic of the nutritive phase. The colony or coenobium is 

 spherical, elongate, or moniliform, though the individuals may 

 retain the primitive homaxonic symmetry (Collosphaeridae) or 

 become flattened (Sphaerozoidae). The skeleton may be absent, 

 spicular, or spheroidal, and the scattered " nuclei " are homogeneous 

 lumps of chromatin. 



The life-history of the Sphaerozoa is still incompletely known, 

 though much has been done by Brandt (1885) to follow it. Accord- 

 ing to this writer three kinds of sexual individuals or colonies 

 occur : isosporous forms, heterosporous forms produced directly, 

 and heterosporous forms produced after gemmation. In the Sphaero- 



