30 THE CHAIN OF LIFE. 



so as to dissolve away the calcite slowly, if the specimen be 

 well preserved, we find that the calcite layers have a very 

 curious structure. This is indicated by the appearance of 

 little white or transparent threads of Serpentine, Dolomite, 

 or Pyroxene, which ramify throughout the substance of the 

 limestone layers, and are left intact when they have been 

 dissolved. These little processes must originally have been 

 pores in the limestone layers, which have been filled with 

 the substance which constitutes the alternate laminae. In 

 addition to this, if we use a somewhat high microscopic power, 

 and especially if we study the structures as seen in thin trans- 

 parent slices, we can perceive a still finer tubulation along the 

 sides of the calcite layers, represented by extremely minute 

 parallel rods of mineral matter (Figs. 17, i8). 



Now if we regard these structures as those of an infiltrated 

 fossil, as described in last chapter, their interpretation will not 

 be difficult. The original organism was composed of calcareous 

 matter in thin concentric laminae, connected with each other 

 by pillars and plates of similar material. Between these 

 laminae was lodged the soft, jelly-like substance of a marine 

 animal, growing by the addition of successive layers, each pro- 

 tected by a thin calcareous crust. The layers were originally 

 traversed by very numerous parallel tubuli, permitting the soft 

 protoplasm to penetrate them ; and when, in the progress of 

 growth, it was necessary to strengthen these layers, they were 

 thickened by a supplemental deposit traversed by larger and 

 ramifying canals. When the animal was dead, and its soft parts 

 removed by decay, the chambers between the laminae, as 

 well as the minute canals and tubuli, became infiltrated with 

 mineral matter, in the manner described in the last chapter, 

 and when so preserved became absolutely imperishable under 

 any. circumstances short of absolute fusion. 



This interpretation leads to the conclusion, at which I arrived 

 from the study of the first well-preserved specimen ever 

 submitted to microscopic examination, that the animal which 



