132 



ANIMAL KINGDOM. 



zooid, though each is organically connected with the others of the 

 same group or shell. The animal is of the simplest possible kind, 

 having generally no mouth or stomach, and no members except slen- 

 der processes of its own substance, which it extrudes through pores in 

 -the shell if it have any. 



The above are shell-making species of Rhizopods. The name Rhizopvds comes from 

 the Greek for root-like feet, — in allusion to the root-like processes they throw ont. The 

 name Furaminifer alludes to the pores. Some of the species not secreting shells (as 

 in the genus Amoeba) have been seen to extemporize a mouth and stomach. When a 

 particle of food touches the surface, the part begins to be depressed, and finally the 

 sides of the depression close over the particle, and thus mouth and stomach are made 

 ■when needed; after digestion is complete, the refuse portion is allowed to escape. 



The shells of some Rhizopods do not consist of distinct cells: the aggregate living 

 mass secretes carbonate of lime, without retaining the distinction of the zooids. This is 

 the case, as Carpenter has observed, in the Nummulite-like genus Orbltolites. Some 

 species make large coral-like masses instead of small shells. 



Other Rhizopods make shell-shaped coverings out of the grains of sand or other mate- 

 rial at hand, agglutinating them. 



Other forms, called Polycystines, secrete siliceous shells; and these shells are sym- 

 metrically radiate or circular. They are common in many seas. Three species, from 



the Barbadoes, are represented in Figs. 

 Figs. 184-186. 184 to 186. Fig. 184, Lychnocanium 



185 ^«^^&»w Lucerna Ehr. ; Fig. 185, Eucyrtidium 



Mongolfieri Ehr. ; Fig. 186, Halicalyp- 

 tra jimbriata Ehr., the first two mag- 

 nified 100 diameters, the last about 75. 

 From these deeply concave forms, there 

 are gradations in one direction to disks 

 with concave centres, and to flat disks, 

 both with plain and pointed borders, 

 and in the other direction to elongate, 

 conical and spindle-shaped forms. 

 Others have the shape of a flattened 

 cross; another is an open diamond, 

 with narrow diagonals and periphery. The disks have a concentric, and not a spiral, 

 structure, and thus are unlike those of Nummulites. For figures, see Ehrenberg's "Mi- 

 krogeologie. " and Bailey in " Amer. Jour. Sci.," II. xxii. pi. 1. 



2. Sponges. — Sponges are regarded as compound animals. The 

 animals, according to H. J. Clark, belong to the division of flagellate 

 Protozoans, a kind (including the genus Monas, etc.) in which there is 

 a short filament (or flagellum) adjoining the mouth. The interior sur- 

 face of the tubes of a sponge is made up of a closely -packed layer of 



Fig. 187. 



184, Lychnocanium Lucerna 'x 100); 185, Eucyr- 

 tidium Mongolfieri (x 100); 186, Ilalicalyptra 

 fimbrtata ( X 75). 



Siliceous spicula of Sponges. 



the zooids, their anterior or mouth extremities projecting freely into 

 the general cavity. The material of the common sponges is ordinarily 

 like horn in its nature; but in most kinds there are minute siliceous" 



