84 THE DAWN OF LIFE. 



the fossil, is undoubtedly that which is typical of Eozoon, yet 

 I find that the acervuline mode of growth, also mentioned 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, are heaped one upon 

 another without any regularity, as is particularly well shown 

 ia some decalcified specimens which I have myself prepared 

 from the slices last put into my hands. I see no indication 

 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 shall I be disposed to regard it as a monstrosity ; since 

 there are many other Foraminifera in which an originally defi- 

 nite 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 chambers, I have 

 little to add to Dr. Dawson's description. The evidence 

 afforded by their internal casts concurs with that of sections, 

 in showing that the segments of the sarcode-body, by whose 

 aggregation each layer was constituted, were but very incom- 

 ])letely divided by shelly partitions ; this incomplete separation 

 (as Dr. Dawson has pointed out) having its parallel in that of 

 the secondary chambers in Carpenteria. But I have occasionally 

 met with instances in which the separation of the chambers 

 lias been as complete as it is iu Foraminifera generally; and 

 the communication between them is then established by seve- 

 ral narrow passages exactly corresponding with those which I 

 have described and figured in Cycloclypeus.* 



" The mode in which each successive layer originates from 

 the one which had preceded it, is a question to which my atten- 

 tion has been a good deal directed ; but I do not as yet feel 

 confident that I have been able to elucidate it completely. 

 There is certainly no regular system of apertures for the 

 jiassage of stolons giving origin to new segments, such as are 

 found in all ordinary Polythalamous Foraminifera, whether 

 their type of growth be rectilinear, spiral, or cyclical; and I 

 am disposed to believe that wliere one layer is separated from 



* Op. cit., p. 294. 



