142 PROTOZOA. 



Foraminifera, it cannot be closely compared with any known type, 

 recent or extinct, belonging to this group of organisms. 



c. The thickness of the calcareous laminae of Eozobn is not only very 

 variable in different specimens, but is liable to great variation even in a 

 single specimen. On the supposition, however, that the calcareous 

 laminae represent the layers of the skeleton of a Foraminifer or other 

 calcareous organism, it would seem very improbable that such great 

 variations in their thickness should be found to exist. 



d. On the hypothesis of the organic nature of Eozobn, there is a strong 

 a priori improbability of such exceedingly minute structures as the 

 " canal-system " of a Foraminiferal test being preserved in rocks so 

 highly crystalline as are the Laurentian limestones. 



e. The canals of the so-called " canal-system " are often flat, instead of 

 round, and are commonly unequal in point of size, while it is not unusual 

 to find them running obliquely to the calcareous laminae instead of trans- 

 versely. These considerations would tend to show that the "canal- 

 system " is of inorganic origin. 



f. The " proper wall " is not truly tubulated, but is formed of minute 

 parallel fibres of serpentine. It is therefore a purely inorganic structure, 

 and is really of the nature of a vein of fibrous serpentine (" chrysotile "). 



Some of the above arguments against the organic nature of Eozobn 

 are of a general nature, and their weight must necessarily remain largely 

 a matter of individual judgment. Others are of a special character, and 

 deal with matters of observation, as to which there are differences of 

 opinion. The special arguments all hinge upon two points— viz., the 

 " canal-system " and the " proper wall " — and with regard to these the 

 following considerations may be indicated : On the view that the 

 " canal-system " is of inorganic origin, it has usually been assumed that 

 it consists of branched fibres of serpentine or of some other silicate, 

 developed in the calcareous laminae. The larger canals are, it is true, 

 commonly filled with serpentine, but it admits of demonstration that the 

 smaller canals are commonly, and in fact usually, occupied simply by 

 crystalline carbonate of lime. On this point, the author is able to fully 

 corroborate the observations of Carpenter and Dawson. In the second 

 place, it can be proved that the so-called " proper wall " of Eozobn is, as 

 a rule, calcareotis, and that it cannot, therefore, be regarded as univer- 

 sally of the nature of fibrous serpentine (chrysotile). This can be best 

 shown by acting with acids on thin vertical sections of Eozobn along a 

 narrow transverse band, leaving the two ends of the section untouched. 

 When this is done, it is found that along the narrow tract acted upon by 

 the acid, not only have the calcareous laminae been dissolved out, but 

 the so-called " proper wall " has at the same time also disappeared, its 

 composition out of carbonate of lime being thus conclusively proved. In 

 some cases, the " proper wall " does not appear to be wholly destroyed 

 by acids, and in such cases it may be supposed that the tubuli of this 

 structure have been injected with serpentine, and have thus been enabled 

 to resist the action of the solvent. The above observation, at any rate, 

 appears to show conclusively that the so-called " proper wall " cannot 

 be always of the nature of a layer or vein of fibrous serpentine (chryso- 

 tile), since it is very commonly and quite unquestionably soluble in weak 

 acids. At the same time, true chrysotile veins often intersect masses of 

 Eozobn, and it is quite probable that in some instances such veins have 

 been confounded with the peculiar striated selvage to the calcareous 

 laminae of Eozobn, which is really what should be understood as the 

 " proper wall." 



