62 introduction to Animal Morphology. 



Radiolaria are divided into two orders : — ist. JMonocyttaria, 

 including the forms with a single central capsule. Tliis in- 

 cludes sixteen families, grouped into three series according 

 as they are devoid of spicules (Nuda), or possess spicules in 

 the ectosarc (Ectolitha), or traversing the central capsule 

 (Entolitha). There is one nude family: — i. Thalassicollidae, 

 with a globular, double contoured, central capsule, often 

 marked polygonally on its surface, including ThalassicoUa. 

 Thalassolampe has no alveoli round the central capsule. 

 Of Ectolitha there are seven families : — 2. Myxobrachidae, 

 including large, soft, floating forms, with one or many con- 

 tractile processes ; the vesicula intima is constricted radially 

 into a number of oval bladders. At the ends of the processes 

 are calcareous concretions, either separate oval, lenticular, or 

 oat-shaped (Coccoliths), or in clusters (Coccospheres). 

 The yellow cells contain starch. These calcareous masses, 

 and others cup-shaped (Cyatholiths) or rod-like (Rhabdo- 

 liths), are found in myriads imbedded in Bathybius, and in 

 the mud of the Atlantic bottom, but nowhere else have they 

 been found organically united to a definite body than in the 

 arms of Myxobrachia {Haeckel). 



3. Thalassosphseridag, with tangential or radial skeleton of 

 ununited, solid (Physematium, &c.), or hollow (Thalasso- 

 planeta) spicules around the central capsule. 4. Aulacan- 

 thidae, with hollow spines, partly tangential, partly radial, 

 serrated, and loosely united. 5. Acanthodesmiadae, with few, 

 loosely united, sometimes ribbon or buckle-like spines. 6. 

 Cystidae, with the tangential skeleton forming conical or cup- 

 like forms, with only one pole closed, and the central capsule 

 at that end ; there may be no mesial constriction (Litharach- 

 nium, &c.), or a longitudinal narrowing, dividing the body into 

 lateral chambers (Petalospyris, &c.), or a transverse constriction 

 (Lithomelissa) or several transverse constrictions(Eucyrtidium), 

 or several both transverse and longitudinal (Botryocampe, &c.), 

 The central capsule is often 4-lobed (Eucecryphalus, &c.) 

 7. Ethmosphaeridae, with a globular, basket-like skeleton, with 

 radiating bars not piercing the central capsule (Heliosphffira). 

 There may be two concentric spheres (Diplosphsera), or more 

 (Arachnosphaera). 8. Aulosphceridae, with hollow, tangential 



