24 Invertebrata. 



particle of protoplasm. The former soon gives way, 

 and the inner portion, freed from external restraints, 

 moves actively by pseudopodia like a Rhizopod (fig. 

 n, D). On reaching a suitable nest this amceboid 

 particle undergoes further development, and becomes 

 a Gregarine like its parent In size these parasites 

 range from the ^Vth to f rds of an inch. 



Class 4. Radiolaria. On examining the material 

 brought up from ocean bottoms, there are frequently 

 found small and beautifully sculptured shells, differing 

 from those of the Foraminifera in that they consist 

 of silica, not of lime, and hence they are compara- 

 tively indestructible by maceration in 

 acids, by which process they can be 

 isolated from the mud wherein they are 

 found. In pattern these shells fre- 

 quently consist of symmetrical, radia- 

 ting rods, united by a variously patterned 

 interweaving of threads of silica, the 

 whole making a network often resem- 

 bling flower-baskets, disks, and perfor- 

 ated spheres, hour-glasses, or helmets. 

 The animals which form these 

 exquisitely ornate little shells are found 

 to be comparatively simple, and in 

 many respects allied to the Rhizopods, 

 shell of a as tn ey sen d out fine thread-like pseu- 

 T dopodia, from the surface layer. The 

 deeper protoplasm is enclosed in a 

 central membranous capsule, perforated with holes, 

 and it contains fat, cellular masses, pigment and often 

 a central vesicle or sac with striped walls; curious 



