Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
410 DESIGN IN NATURE<br />
except in their colour and in the clearness of their protoplasm, and, like the white corpuscles, they are capable ot<br />
amoeboid movement, and of undergoing multipUcation by division. The colourless corpuscles appear to be formed<br />
in great number in the embryonic liver as soon as this is developed, as well as in the lymphatic glands, spleen, and<br />
thymus gland. It has been supposed that the colourless corpuscles formed in these organs acquire colour, and are<br />
converted into nucleated red corpuscles, but there is no direct evidence in favour of this view.<br />
" The primary nucleated red corpuscles are at length succeeded by smaller disc-shaped red corpuscles without<br />
nuclei, having all the characters of the blood-discs of the adult. This substitution proceeds gradually, until, long<br />
before the end of intra -uterine life, the nucleated red corpuscles have almost entirely vanished from the blood. The<br />
disc-shaped red corpuscles are produced in the interior of angioblastic connective tissue cells in the following<br />
manner :—A part of the protoplasm of the cell acquires a reddish tinge, and after a time the coloured substance<br />
becomes condensed in the form of globules within the cells, varying in size from a minute speck to a spheroid of<br />
the diameter of a blood-corpuscle, or even larger ; but gradually the size becomes more uniform. Some parts ot<br />
the embrvonic connective tissue, especially where a vascular tissue, such as the fat, is about to be developed are<br />
completely studded with cells hke these, occupied by a number of coloured spheroids and formmg nests ot blood-<br />
blood-islands.' After a time the cells become elongated and pointed at their ends, and<br />
corpuscles or minute '<br />
processes grow out to join prolongations of neighbouring blood-vessels or of similar cells. _ At the same time<br />
vacuoles form within them, and becoming enlarged coalesce to form a cavity filled with fluid, m which the reddish<br />
globules, which are now becoming disc-shaped, float. Finally the cavity extends through the cell-processes into<br />
those of neighbouring cells, and a vascular network is produced, and this becomes eventually united with pre-<br />
existing blood-vessels, so that the blood-corpuscles which have been formed within the cells in the manner described<br />
get into the general circulation." ^<br />
The " intracellular " mode of development of the red blood-corpuscles in most animals ceases at or before birth.<br />
They are supposed to be developed after birth (in the growing child and adult) from the red marrow of the bones,<br />
especially that of the ribs, and from the leucocytic marrow-cells called erythroblasts . This view is, however, disputed,<br />
and the erythroblasts, according to Bizzozero, are not developed from the leucocytic marrow-cells, nor from the<br />
white corpuscles of the blood, but are corpuscles sui generis, which multiply by karyokinesis, and become gradually<br />
transformed in the mammaha, with the disappearance of the nucleus, into the red blood discs.<br />
This view is favoured by Professor Schafer, who states that the coloured cells observed by him " have almost<br />
always been distinctly smaller than the ordinary marrow-cells, often of irregular forms, and sometimes appear to<br />
be undergoing division. They are amoeboid cells, the protoplasm of which is coloured by haemoglobin, and they<br />
closely resemble the nucleated red blood-corpuscles of the embryo. It appears, therefore, probable that the cells<br />
in question are descendants of the embryonic red blood-corpuscles, and that they are transformed into the ordinary<br />
blood-discs by the gradual atrophy and disappearance of the nucleus and the moulding of the coloured cell-substance<br />
into the shape of the bi-concave red corpuscles." It will be observed that the series of changes which result in the<br />
formation of blood and blood-vessels are self-inaugurated, and in no way influenced by irritability, external stimuli,<br />
or environment.<br />
The production of young blood is especially interesting in its relation to the capillary blood-vessels ; the blood<br />
and the channels through which it is to flow being practically developed at the same time. The simultaneous<br />
development is an important feature as indicating design. The blood-vessels and their contents are evidently part<br />
of a general scheme.<br />
Similar arrangements are witnessed in the growth of young bone, which may be developed in membrane or in<br />
cartilage. In the flat bones of the head (membranous to begin with), such as the frontal and parietal, the membranes<br />
are stiffened by the deposition of lime (earthy salts). This lime is not, however, scattered all over the bones. On<br />
the contrary, it radiates from an appointed centre stellate-fashion, and spreads towards the periphery of the bones.<br />
In like manner the long bones which have their origin in hyaline cartilage have separate centres of ossification ;<br />
centres increasing according to age until puberty is reached. Thus in the femur or thigh bone, the first centre<br />
of ossification appears in the middle of the shaft about the beginning of the third month after impregnation. In<br />
this case the ossification extends up and down the shaft before the other centres appear. Towards the end of foetal<br />
life a second centre appears at the lower portion of the bone and forms part of the knee-joint. A year after birth,<br />
a third centre appears at the upper end of the bone and assists in forming the hip joint. During the fourth year<br />
a fourth centre appears and forms the knob known as the trochanter major; a fifth centre appearing during the<br />
fourteenth or fifteenth year to form the trochanter minor. The thigh bone is thus developed from five centres (the<br />
sacrum has as many as thirty-three centres). The shaft or body of the bone is called the " diaphysis " ; the other<br />
parts being designated the " epiphyses." In all this there is marked order and strict adherence to a building plan ;<br />
1 Quain's " Elenients of Anatomy," edited by E. A. Scliafev, LL.D., F.R.S., and George Dancer Tliane, vol. i. part ii. 1898, pp. 217-219.<br />
the