SECT. ii. THE AULOCANTHA. 21 



In certain Polycystina, the perforations of the shell 

 are so large and so close together, that the sarcode body 

 of the animal appears to be covered by a siliceous net. 

 This connects them with the Thalassicollse, minute crea- 

 tures found passively floating on the surface of the sea. 

 Th. morum, which is one of the most simple of the few 

 forms known, has a spherical body of sarcode covered 

 with a siliceous net, through which the pseudopodia 

 radiate in all directions, as in the Actinophrys, but it is 

 studded at regular distances with groups of apparently 

 radiating siliceous spicules. 



The Aulocantha scolymantha (fig. 92), found by M. 

 Haeckel in the Mediterranean, may be taken as an 

 example of the most general form of the Thalassicolla. 

 The siliceous skeleton of some of the Radiolaria re- 

 sembles the Chinese ivory toy of ball within ball. That 

 of the Actinomma drymodes (fig. 93) consists of three 

 perforated concentric spheres, with six strong spicules 

 attached to the outer surface, perpendicular to one 

 another and prolonged in the interior to the central 

 sphere. Hundreds of finer bristle-like spicules radiate 

 from the surface. The animal is chiefly contained in 

 the central sphere, and from it a perfect forest of fine, 

 long pseudopodia radiate in thick tufts through the 

 apertures of the exterior sphere. 



The skeleton of the Haliomma (fig. 94) consists of only 

 two concentric spheres. In many species of Haliomma 

 and Actinomma the animals are of the most vivid ver- 

 milion or purple colour. Little or nothing is known 

 of the reproduction of these microscopic organisms. 



The Actinomma drymodes and the Haliomma are two 

 of the most beautiful microscopic rhizopods discovered 

 by M. Haeckel. 



There is a family of fresh- water testaceous rhizopods 

 of which one group secretes its shell and the other builds 

 it. The horny shell secreted by the group of the Arcella 



