120 THE DAWN OF LIFE 



organized. One of these, Actinophrys (Fig. 9), has the body 

 globular and unchanging in form, the outer wall of greater thick- 

 ness ; the pulsating vesicle like a blister on the surface, and the 

 pseudopods long and thread-like. Its habits are similar to 

 those of the Amoeba, and I introduce it to show the variations^ 

 of form and structure possible even among these simple 

 creatures. 



The Amoeba and Actinophrys are fresh-water animals, and 

 are destitute of any shell or covering. But in the sea there ex- 

 ist swarms of similar creatures, equally simple in organization, 

 but gifted with the power of secreting around their soft bodies 

 beautiful little shells or crusts of carbonate of lime, having one 

 orifice, and often in addition multitudes of microscopic pores 

 through which the soft gelatinous matter can ooze, and form 

 outside finger-like or thread-like extensions for collecting food. 

 In some cases the shell consists of a single cavity only, but in 

 most, after one cell is completed, others are added, forming 

 a series of cells or chambers communicating with each other, 

 and often arranged spirally or otherwise in most beautiful and 

 symmetrical forms. Some of these creatures, usually named 

 Foraminifera, are locomotive, others sessile and attached. 

 Most of them are microscopic, but some grow by multiplication 

 of chambers till they are a quarter of an inch or more in 

 breadth. 



The original skeleton or primary cell wall of most of these 

 creatures is seen under the miscroscope to be perforated with 

 innumerable pores, and is extremely thin. When, however, 

 owing to the increased size of the shell or other wants of the 

 creature, it is necessary to give strength, this is done by add- 

 ing new portions of carbonate of lime to the outside, and to 

 these Dr. Carpenter has given the appropriate name of " sup- 

 plemental skeleton " ; and this, when covered by new growths, 

 becomes what he has termed an " intermediate skeleton." The 

 supplemental skeleton is also traversed by tubes, but these are 



