196 



PROTOZOA. 



(fig. 123); HALIOMMID^E with latticed spheres (fig. 85); DISCID.E, disc 

 like. 



Sub Order II. ACANTHARIA. Capsular membrane perforated every- 

 where by pore canals; twenty spines of acanthin which radiate from the 

 centre in an extremely regular manner, form the skeleton, as in Acantho- 

 metra (fig. 125), or the spines are bound together by a latticed sphere 

 formed of twenty separate plates, as in Acanthophracta. 



Sub Order III. MONOPYLEA or NASSELLARIA. The pores of the 

 central capsule occupy a pore field at one end. Best known are the CYRTID.E 

 (Eucyrtidium, fig. 124) with graceful helmet or cage-like skeletons. 



Sub Order IV. PH^EODARIA. The central capsule has a principal 

 opening, often drawn out into a tube and surrounded by dark pigment 

 (phteodium) around which may be smaller openings. The skeleton is sili- 

 cious and formed of hollow pieces. Mostly from the deep seas. Aida- 

 cantha, Aulosphcera, Ccelodendron, measuring from 0.5 to 1.0 mm., are 

 pelagic. 



Order V. Foraminifera (Thalamophora, Reticularia). 

 The Foraminifera, though not equalling the Radiolaria in 

 beauty and variety of forms, excel them in numbers of indi- 

 viduals, and hence have a greater importance in the history of the 

 earth. No group of animals at present or in the past have had 

 so great a part in the formation of beds of rock. 



The most prominent characteristic of the order is afforded by 

 the shell. This is an envelope, closed 

 at one pole, and usually opening to the 

 exterior at the other, the pseudopodia 

 passing through the aperture (fig. 128). 

 Accordingly as the axis connecting 

 these poles is shortened or lengthened, 

 the shell becomes disc-like, spherical, 

 flask formed or even coiled in a spiral. 

 An additionalfeature, the division of the 

 interior of the shell by transverse par- 

 titions into numerous chambers, is com- 

 mon. Such many-chambered shells 

 (Polythalamia) are at first small, and 

 consist of one or few chambers, but 

 FIG. 128. Ouadruia symmetrica. as the animal grows new chambers are 



(After F. E. Schulze.) cv, con- 

 tractile vacuoie; n, nucleus; continually added at the mouth 01 the 

 JV, food-body. v -n X AI 11 . * ^i 



stiell. Openings in the walls of the 



shell (foramina) connect the adjacent chambers. The spiral 

 shells with many chambers have a striking resemblance to the 

 much larger shells of the Nautilus (fig. 386), which led to the 

 view once held that the Foraminifera were small cephalopoda. 



