60 PEOCEBDINGS OF THE GEOLOGICAL SOCIETT. [NoV. 23, 



quence of the complete infiltration of tlie chambers and canals, 

 originally occupied by the sarcode-body of the animal, by mineral 

 matter insoluble in dilute nitric acid, the removal of the calcareous 

 shell brings into view not only the internal casts of the chambers, 

 but also casts of the interior of the " canal-system" of the " inter- 

 mediate " or " supplemental skeleton," and even casts of the interior 

 of the very fine parallel tubuli Avhich traverse the proper walls of 

 the chambers. And, as I have remarked elsewhere *, " such casts 

 place before us far more exact rej^resentations of the configuration of 

 the animal body and of the connexions of its different parts, than 

 we could obtain even from living specimens by dissolving-away their 

 shells with acid ; its several portions being disposed to heap them- 

 selves together in a mass when they lose the support of the calca- 

 reous skeleton." 



The additional opportunities I have thus enjoyed mil be found, I 

 believe, to account satisfactorily for the difierences to be observed 

 between Br. Dawson's account of the Eozoon and my own. Had I 

 been obliged to form my conclusions respecting its structure only 

 from the specimens submitted to Dr. Dawson, I should very probably 

 have seen no reason for any but the most complete accordance with 

 his description : while if Dr. Dawson had enjoyed the advantage of 

 examining the entire series of preparations which have come under 

 my own observation, I feel confident that he would have anticipated 

 the corrections and additions which I now ofi'er. 



Although the general plan of groivth described by Dr. Dawson, 

 and exhibited in his photographs of vertical sections of the fossil 

 (PI. VI., PI. YII. fig. 1), is undoubtedly that which is typical 

 of Eozoon, yet I find that the acervuUne mode of growth, also men- 

 tioned by Dr. Dawson, very frequently takes its place in the more 

 superficial parts, where the chambers, which are arranged in regular 

 tiers in the laminated portions (PI. VIII. fig. 1), are heaped one 

 upon another without any regularity, as is particularly well shown 

 in some decalcified specimens which I have myself prepared from 

 the shoes last put into my hands (PI. IX. fig. 2). I see no indi- 

 cation that this departure from the normal type of structure has 

 resulted from an injury ; the transition from the regular to the 

 irregular mode of increase not being abrupt, but gradual. Nor 

 should I be disposed to regard it as a monstrosity ; since there are 

 many other Foraminifera in which an originally definite plan of 

 growth gives place in a later stage to a like acervuline piling-up of 

 chambers. 



In regard to the form and relations of the cJiambers, I have little 

 to add to Dr. Dawson's description. The evidence afforded by their 

 internal casts (PL IX. fig. 1) concurs with that of sections, in showing- 

 that the segments of the sarcode-body, by whose aggregation each 

 layer was constituted, were but very incompletely divided by shelly 

 partitions ; this incomplete separation (as Dr. Dawson has pointed 

 out) having its parallel in that of the secondary chambers in Ckirpen- 

 teria. But I have occasionally met with instances in which the 

 * Introduction to the Study of the Foraminifera, p. 10. 



