William Benjamin Carpenter

“ There can be no doubt that, in common with all the lower forms of animal as well as vegetable life, the Rhizopoda tend to multiply by a separation of continuously-growing parts of their bodies, which may take the form either of fission or of gemmation, according as the original body undergoes subdivision, or as it puts forth an extension which eventually detaches itself. ”

“ Our own experience of the wide limits within which any specific group of the Foraminifera multiply their varietal forms, related by some peculiar conditions of growth and ornamentation, has led us to concur fully with those who regard nearly every species of Foraminifera as capable of adapting itself, with endless modifications of form and structure, to very different habitats in brackish and in salt water ”

“ Again, I have shown (2nd series) that a parallel variation is displayed by the genus Orbiculina, whose ordinarily helical plan of growth has caused M. D'Orbigny to range it among his Helicostègues, notwithstanding that in fully developed specimens its mode of growth is not unfrequently cyclical. The occasional exchange in this type of one plan of increase for the other, at an advanced period of life, is a fact of very high interest; for when an Orbiculina has undergone this change, the outer or cyclical portion of its disk can in no way be distinguished from that of Orbitolites ”

“ Now it may be at once conceded that no other group in the Animal kingdom affords any thing like the same evidence, on the one hand, of the derivation of a vast multitude of distinguishable forms from a few primitive types, and on the other, of the continuity of those types through a vast succession of geological epochs. ”

“ There is, moreover, a negative character of much importance, which is naturally associated with the absence of differentiation,—namely, the deficiency of the "nucleus" and "contractile vesicle" that occur both in Actinophrys and in Amœba. So far as is yet known, there is a perfect agreement as to all these characters between the Foraminifera and the Gromida; and I regard Lieberkühnia as standing in the same relation to the chitine-covered Gromia or to the calcareous-shelled Foraminifera, that Actinophrys does to the chitine-covered Euglypha or to the siliceous-shelled Polycystina. ”

“ Now on this I have to remark, in the first place, that the two families Amœbina and Actinophryna, which are associated in the order Proteina, differ essentially from each other in several particulars which seem to me of great; physiological importance; whilst I cannot trace any such peculiar bond of union between them, as would be required to justify their separation from all other Bhizopods and their association into a separate order. ”

“ A somewhat parallel case, however, as regards the first of these points, is presented by certain of the humbler groups of the Vegetable kingdom, in which it is becoming more and more apparent, from the careful study of their life-history, not only that their range of variation is extremely wide, but that a large number of reputed genera and species have been erected upon no better foundation than that afforded by the transitory phases of types, hitherto known only in their states of more advanced development. ”

“ It can scarcely, I think, be questioned that such a continuity of the leading types of Foraminifera maintained through so long a series of geological periods, and the recurrence of similar varietal departures from those types, is a result of the facility with which creatures of such low and indefinite organization adapt themselves to a great variety of external conditions; so that, on the one hand, they pass unharmed through changes in those conditions which are fatal to beings of higher structure and more specialized constitution ”

“ A careful examination of the substance of the Actinophrys serves to explain this apparent inconsistency; for it thence appears that the body and its pseudopodian extensions are far from having the homogeneousness of those of Lieberkühnia, but that there is an incipient differentiation of their substance into two dissimilar constituents, the outer layer being least granular and of firmer consistence, whilst the contained portion approaches more nearly to the character of a liquid, as may be seen by the freer movements of the granular particles which are suspended in it. ”

“ And it is to be specially observed that all those forms in which it is at present known to attain its greatest completeness, are those tropical or semi-tropical types, in which the influence of warmth, abundance of food, and other external agencies in promoting development, appear specially to favour the largest growth and the most specialized evolution of the Foraminiferous type. ”

“ Incipient differentiation of the protoplasmic substance into endosarc and ectosarc, the former semi-fluid and granular, the latter more tenacious and pellucid; a nucleus and contractile vesicle; pseudoppdia rod-like, usually tapering from base to point, composed of the same substance as the ectosarc, exhibiting little disposition either to ramify or to coalesce, haying a more or less regular radiating arrangement, and not showing any constant circulation of granules in their subatance, although a movement of particles adherent to their exterior is often to be distinguished. ”

“ Hence the idea of the derivation of Orbitolites and Orbiculina from the same original must be admitted to be scarcely less probable than that of the derivation of the helical and the cyclical forms of Orbiculina, or of the simple and complex types of Orbitolites, from a common parentage.
Let us now apply the same mode of inquiry to Alveolina. I have shown (2nd series) that this organism is closely allied in every other respect than its geometrical plan of growth to the types we have just been considering ”

“ Each segment of the body has its own proper envelope, so that the septa between the chambers are composed of two distinct laminæ, which diverge from each other where they give passage to the canal system, and which are often further separated by the intervention of a portion of the intermediate skeleton. The passages of communication between the chambers are so narrow, that segments of the body are much more isolated from each other than they are in the type already described ”

“ But further, I showed that a distinction on which almost any naturalist would feel justified in relying, as of specific if not of generic value, that between the simple type in which all the cells are arranged on only one plane, and the complex type in which there are two superficial planes more or less strongly differentiated from the median, is no less invalid. ”

“ T. Rupert Jones and W. K. Parker, [9] those gentlemen have felt themselves justified, on the like grounds in reducing a multitude of reputed genera and species to a single type. Between the nautiloid Cristellariæ and the straight moniliform or rod-like Nodosariæ, which agree in essential characters of structure and mode of growth, they find such a continuous series of connecting links, that no line of demarcation can be anywhere drawn, the straight, the curved, and the spiral forms passing gradationally one towards another ”

“ The communications between the successive chambers, and between the last chambers and the exterior (whether formed by a single large aperture as in Miliola, or by the multiplication of smaller pores as in Peneroplis,) are very free; having to give passage not merely to stolons which are subservient to the multiplication of segments, but to bands of sarcode-substance large enough to transmit with facility, to the segments that are furthest removed from the exterior, the nutrient materials obtained by the pseudopodia which issue from the last alone. ”

“ For, as has just been shown, a longer continuance of the helical mode of growth in which Orbitolites often commences, would really produce an Orbiculina, with its centre so invested by successive whorls as to form a vertical linear axis; and we find this axis in Orbiculina, sometimes equalling in length the diameter of the spire, so that this organism at an early stage of its growth may be nearly spheroidal. ”

“ The differentiation between this group and the one in which the shell, being everywhere perforated with pores more or less fine, allows the passage of pseudopodia from every part of the surface of the body, I hold, with Dujardin, to be of essential importance. ”

“ For the endless gradational departures from any types which we may assume as fixed, and the occurrence of links of connexion between such as present the best marked differentiations, seem to me to point unmistakeably to this as the only escape from that difficulty of indefinite multiplication, which attends the application of the doctrine of distinct specific creations to a group in which scarcely any two individuals are alike. ”

“ For Dujardin distinctly recognized the fact that Arcella and Difflugia are nothing else than testaceous Amœbans; and in separating these from those Rhizopods which are characterized by the possession of filiform, tapering, or ramifying pseudopodia, he laid the foundation of a truly natural grouping of the latter. ”

“ Further, I have shown that the development of this supplemental skeleton is, in a great degree, independent of that of the spire; hence, if this last be the essential component of the organism (as all analogy indicates) , the supplemental skeleton must be regarded as a feature of minor importance. On the other hand, the development of radiating out-growths is an occurrence not unfrequent among other helicine Foraminifera, even in species whose typical form is altogether destitute of them (as Professor Williamson has pointed out in Polystomella crispa) ”

“ Thus we have found strong reason for regarding temperature as exerting a most important influence in favouring, not merely increase of size, but specialization of development; all the most complicated and specialized forms at present known being natives either of tropical or of sub-tropical seas, and many of these being represented in the seas of colder regions by comparatively insignificant examples, which there seems adequate reason for regarding as of the same specific types with the tropical forms, even though deficient in some of their apparently most important features. ”

“ This second section was subdivided by Dujardin into three tribes; the first composed of the genera Trinema, Euglypha, and Gromia (all discovered by himself) , which are distinguished from Difflugia only by the attenuation of their pseudopodia; the second is composed of the single genus Miliola, which agrees with the ordinary Foraminifera in the possession of a calcareous shell, whilst it corresponds with Gromia in having but a single large aperture from which the pseudopodia extend themselves ”

“ There is no definite line of demarcation between them; but the one graduates insensibly into the others. It seems to be, however, from the ectosarc alone that the pseudopodia are put forth; the granular endosarc not extending itself into them. A movement of granules along their surface may indeed be discerned by careful observation; but these appear to be merely particles which have been entrapped by adhesion to the surface of the pseudopodia, and are being transmitted to the body ”

“ The size of the greater part of these organisms is so small, that many hundreds, thousands, or even tens of thousands of them, may be contained in a pill-box; and yet it is usually not too minute to prevent the practised observer from distinguishing the most important peculiarities of each individual by a hand-magnifier alone, or from dealing with it separately by a very simple kind of manipulation. Hence the systematist can easily select and arrange in series such of his specimens as display sufficient mutual conformity, whilst he sets apart such as are transitional or osculant ”

“ Now however improbable it may seem at first sight that an Orbitolites, which extends itself as a flat or bi-concave disk by successive concentric growths, and an Alveolina acquiring a fusiform shape by successive turns round a progressively elongating axis, should have a common original, yet, when the intermediate links are duly studied, a continuous gradation is found to be established. ”

“ For although these types are usually distinguishable the one from the other without the least difficulty, yet they are often combined in the same individuals, and this in such a variety of modes, that the transition from the simple to the complex may be clearly seen, by the comparison of a sufficient number of specimens, to be by no means attributable to a mere advance of age. ”

“ On this view, these animals have their ventral constantly differentiated from their dorsal surface, it being from the former alone that the pseudopodian extensions proceed; and thus a transition would seem to be indicated towards the testaceous Amœbina (Arcella, Difflugia, &c.) in which the dorsal surface is invested by a shell, and the pseudopodia are strictly limited to the ventral region. ”

“ In the one case, as in the other, the direct evidence of descent affords cogent evidence as to the possible extent of modification within the limits of particular races; and when that evidence is brought into relation with analogous facts in regard to the yet greater variations of which we have direct evidence in the case of domesticated animals, it points to conclusions of higher generality, which physiologists find no difficulty in accepting. ”

“ Again, there are certain Polythalamia, the successive chambers of whose shells, although formed by continuous gemmation the one from the other, are so slightly connected as to be easily separable by accidental violence, and of which the animals can maintain their lives just as well when they are thus broken up into distinct segments as when retaining their original continuity ”