106 THE SEA SHORE 



lime, having thus the same chemical composition as chalk, lime- 

 stones, and marble. 



If hydrochloric acid be added to some of these shells, they are 

 immediately attacked by the acid and are dissolved in a very short 

 time, the solution being accompanied by an effervescence due to the 

 escape of carbonic acid gas. 



The shells vary in size from about one-twelfth to one 

 three-hundredth of an inch, and consist either of a single chamber, 

 or of many chambers separated from each other by perforated 

 partitions of the same material. Sometimes these chambers are 

 arranged in a straight line, but more frequently in the form of a 

 single or double spiral. In some cases, however, the arrangement 

 of chambers is very complex. 



We have already referred to the fact that the shells present a 

 number of perforations on the exterior, in addition to those which 



FIG. 55. A SPIRAL FORAMINIFER FIG. 56. A FORAMINIFER our OF 

 SHELL ITS SHELL 



pierce the partitions within, and it is this characteristic which has 

 led to the application of the name Foraminifera (hole -bearing) to 

 the little beings we are considering. 



The animal inhabiting the shell is exceedingly simple in struc- 

 ture, even more so than the amoeba. It is merely a speck of proto- 

 plasm, exhibiting hardly any differentiation nothing, in fact, save 

 a contractile cavity (the vacuole), and numerous granules that 

 probably represent the indigestible fragments of its food. 



The protoplasm fills the shell, and also forms a complete gela- 

 tinous covering on the outside, when the animal is alive ; and the 

 vacuole and granules circulate somewhat freely within the semi- 

 solid mass. Further, the protoplasm itself is highly contractile, 

 as may be proved by witnessing the rapidity with which the animal 

 can change its form. 



When the foraminifer is alive, it floats freely in the sea, with a 

 comparatively long and slender thread of its substance protruded 



