66 THE DAWN OF LIFE. 



Huxley the name BathybiuSj and which is believed to be 

 a protozoon of indefinite extension, though it may 

 possibly be merely the pulpy sarcode of sponges and 

 similar things penetrating the ooze at their bases. On 

 this primary layer grew a delicate calcareous shell, per- 

 forated by innumerable minute tubuli, and by some 

 larger pores or septal orifices, while supported at inter- 

 vals by perpendicular plates or pillars. Upon this again 

 was built up, in order to strengthen it, a thickening 

 or supplemental skeleton, more dense, and destitute of 

 fine tubuli, but traversed by branching canals, through 

 which the soft gelatinous matter could pass for the 

 nourishment of the skeleton itself, and the extension of 

 pseudopods beyond it. (Fig. 10.) So was formed the 

 first layer of Eozoon, which seems in some cases to 

 have spread by lateral extension over several inches 

 of sea bottom. On this the process of growth of succes- 

 sive layers of animal sarcode and of calcareous skeleton 

 was repeated again and again, till in some cases even a 

 hundred or more layers were formed. (Photograph, 

 Plate III., and nature print, Plate V.) As the process 

 went on, however, the vitality of the organism became 

 exhausted, probably by the deficient nourishment of 

 the central and lower layers making greater and greater 

 demands on those above, and so the succeeding 

 layers became thinner, and less supplemental skeleton 

 was developed. Finally, toward the top, the regular 

 arrangement in layers was abandoned, and the cells 

 became a mass of rounded chambers, irregularly piled 

 up in what Dr. Carpenter has termed an "acervuline " 



