6 



COMPARATIVE ANATOMY 



CHAP. 



Sub-Class III. Heliozoa. 



Globular Sarcodina, naked or clothed with a siliceous skeleton, with fine more 

 or less stiff pseudopodia radiating on all sides. Contractile vacuoles generally 



present in varying numbers. Actinophrys 

 (Fig. 4), Actinosphcerium, Acanthocystis, Clath- 

 rulina. 



Sub-Class IV. Radiolaria. 



Body divided by an originally spherical or 

 egg-shaped capsular membrane into an outer, 

 and an inner, nucleated portion (outer and 

 inner capsules). The outer capsule consists of 

 protoplasm (without nucleus) and of a gela- 

 tinous envelope (calymna). The protoplasm 

 forms a layer round the inner capsule and a 

 network round the calymna, these two being 

 connected by means of protoplasmic threads. 



FIG. 4.-Actinophrys sol, after Gre- Fineflexible pseudopodia radiate in all directions 

 nacher. p, Pseudopodia ; n, nucleus ; , x _. , 



axial filaments of the pseudopodia. fl ' om the surface ot the calymna. Skeletons 



of extraordinarily various shapes, of silica or of 



chitin-like organic substance (acanthin), are seldom wanting. The extra- and intra- 

 capsular protoplasm are connected through various openings in the cell-membrane. 



This division of the marine Sarcodina is wonderfully rich 

 in forms and shapes. Without contractile vacuoles. Uni- 

 cellular algte (yellow cells) live symbiotically with the 

 Radiolaria. The family of the Polycyttaria among the 

 Spumellaria is distinguished by the formation of colonies. 



A. Porulosa. 



Central capsule spherical, without a principal aperture, 

 with innumerable fine pores. 



I. Spumellaria. Nucleus central, dividing late in the 

 life of the individual. Skeleton siliceous or wanting, never 

 penetrating into the intra-capsular protoplasm. Thalassi- 

 colla, Collozoum, Spliccrozoum, Thalassoplancta (Fig. 5), 

 Collosphccra, Didyastrum. 



II. Acantharia. Nucleus eccentric, dividing early. 



.. ' 

 " 



r \: 



FIG. 5. Thalassoplancta 

 brevispicula, part of a sec- 

 tion, after Haeckel. km, 

 Capsular membrane ; ip, 

 intra-capsular ; ep, extra- 

 capsular protoplasm ; i\, 

 nucleus; nl, nucleoli ; ot, FIG. G. Phractaspis prototypus (after Haeckel), skeleton. 



oil-drops ; en, alveolar ca- 

 lymna ; rp, protoplasm ou Skeleton of acanthin, radiating from the centre of the 

 the surface of the calymna ; n m. i /T?- c\ 

 s> S picules. central capsule. Acanthometra, Phractaspis (tig. 6). 



