life is dawn on the earth 13

life is dawn on the earth 13

"Since the above was written, thick slices of Eozoon from Grenville

have been prepared, and submitted to the action of hydrochloric acid

until the carbonate of lime was removed. The serpentine then remains

as a cast of the interior of the chambers, showing the form of their

original sarcode-contents. The minute tubuli are found also to have

been filled with a substance insoluble in the acid, so that casts

of these also remain in great perfection, and allow their general

distribution to be much better seen than in the transparent slices

previously prepared. These interesting preparations establish the

following additional structural points:--

 

"1. That the whole mass of sarcode throughout the organism was

continuous; the apparently detached secondary chambers being, as

I had previously suspected, connected with the larger chambers by

canals filled with sarcode.

 

"2. That some of the irregular portions without lamination are not

fragmentary, but due to the acervuline growth of the animal; and that

this irregularity has been produced in part by the formation of

projecting patches of supplementary skeleton, penetrated by beautiful

systems of tubuli. These groups of tubuli are in some places very

regular, and have in their axes cylinders of compact calcareous

matter. Some parts of the specimens present arrangements of this kind

as symmetrical as in any modern Foraminiferal shell.

 

"3. That all except the very thinnest portions of the walls of

the chambers present traces, more or less distinct, of a tubular

structure.

 

"4. These facts place in more strong contrast the structure of

the regularly laminated species from Burgess, which do not show

tubuli, and that of the Grenville specimens, less regularly

laminated and tubulous throughout. I hesitated however to regard

these two as distinct species, in consequence of the intermediate

characters presented by specimens from the Calumet, which are

regularly laminated like those of Burgess, and tubulous like those

of Grenville. It is possible that in the Burgess specimens, tubuli,

originally present, have been obliterated, and in organisms of this

grade, more or less altered by the processes of fossilisation, large

series of specimens should be compared before attempting to establish

specific distinctions."

 

 

(B.) Original Description of the Specimens added by Dr. Carpenter to

the above--in a Letter to Sir W. E. Logan.

 

[_Journal of Geological Society_, February, 1865.]

 

"The careful examination which I have made, in accordance with

the request you were good enough to convey to me from Dr. Dawson

and to second on your own part, with the structure of the very

extraordinary fossil which you have brought from the Laurentian

rocks of Canada,[Q] enables me most unhesitatingly to confirm the

sagacious determination of Dr. Dawson as to its Rhizopod characters

and Foraminiferal affinities, and at the same time furnishes new

evidence of no small value in support of that determination. In

this examination I have had the advantage of a series of sections

of the fossil much superior to those submitted to Dr. Dawson; and

also of a large series of decalcified specimens, of which Dr. Dawson

had only the opportunity of seeing a few examples after his memoir

had been written. These last are peculiarly instructive; since

in consequence of the complete infiltration of the 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 'intermediate' or 'supplemental skeleton,' and even casts of

the interior of the very fine parallel tubuli which traverse the

proper walls of the chambers. And, as I have remarked elsewhere,[R]

'such casts place before us far more exact representations of the

configuration of the animal body, and of the connections 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 themselves together in a mass when they lose the

support of the calcareous skeleton.'

 

[Footnote Q: The specimens submitted to Dr. Carpenter were taken from a

block of Eozoon rock, obtained in the Petite Nation seigniory, too late

to afford Dr. Dawson an opportunity of examination. They are from the

same horizon as the Grenville specimens.--W. E. L.]

 

[Footnote R: _Introduction to the Study of the Foraminifera_, p. 10.]

 

"The additional opportunities I have thus enjoyed will be found,

I believe, to account satisfactorily for the differences to be

observed between Dr. 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 offer.

 

"Although the general plan of growth described by Dr. Dawson, and

exhibited in his photographs of vertical sections of 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 in 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 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 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 incompletely 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 has been as complete as it is in Foraminifera generally; and

the communication between them is then established by several narrow

passages exactly corresponding with those which I have described and

figured in Cycloclypeus.[S]

 

[Footnote S: _Op. cit._, p. 294.]

 

"The mode in which each successive layer originates from the one

which had preceded it, is a question to which my attention 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 passage 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 where one layer is

separated from another by nothing else than the proper walls of

the chambers,--which, as I shall presently show, are traversed by

multitudes of minute tubuli giving passage to pseudopodia,--the

coalescence of these pseudopodia on the external surface would

suffice to lay the foundation of a new layer of sarcodic segments.

But where an intermediate or supplemental skeleton, consisting of a

thick layer of solid calcareous shell, has been deposited between

two successive layers, it is obvious that the animal body contained

in the lower layer of chambers must be completely cut off from

that which occupies the upper, unless some special provision exist

for their mutual communication. Such a provision I believe to have

been made by the extension of bands of sarcode, through canals left

in the intermediate skeleton, from the lower to the upper tier of

chambers. For in such sections as happen to have traversed thick

deposits of the intermediate skeleton, there are generally found

passages distinguished from those of the ordinary canal-system by

their broad flat form, their great transverse diameter, and their

non-ramification. One of these passages I have distinctly traced

to a chamber, with the cavity of which it communicated through two

or three apertures in its proper wall; and I think it likely that

I should have been able to trace it at its other extremity into a

chamber of the superjacent tier, had not the plane of the section

passed out of its course. Riband-like casts of these passages are

often to be seen in decalcified specimens, traversing the void spaces

left by the removal of the thickest layers of the intermediate