410 DESIGN IN NATURE 



except in their colour and in the clearness of their protoplasm, and, like the white corpuscles, they are capable ot 

 amoeboid movement, and of undergoing multipUcation by division. The colourless corpuscles appear to be formed 

 in great number in the embryonic liver as soon as this is developed, as well as in the lymphatic glands, spleen, and 

 thymus gland. It has been supposed that the colourless corpuscles formed in these organs acquire colour, and are 

 converted into nucleated red corpuscles, but there is no direct evidence in favour of this view. 



" The primary nucleated red corpuscles are at length succeeded by smaller disc-shaped red corpuscles without 

 nuclei, having all the characters of the blood-discs of the adult. This substitution proceeds gradually, until, long 

 before the end of intra -uterine life, the nucleated red corpuscles have almost entirely vanished from the blood. The 

 disc-shaped red corpuscles are produced in the interior of angioblastic connective tissue cells in the following 

 manner :— A part of the protoplasm of the cell acquires a reddish tinge, and after a time the coloured substance 

 becomes condensed in the form of globules within the cells, varying in size from a minute speck to a spheroid of 

 the diameter of a blood-corpuscle, or even larger ; but gradually the size becomes more uniform. Some parts ot 

 the embrvonic connective tissue, especially where a vascular tissue, such as the fat, is about to be developed are 

 completely studded with cells hke these, occupied by a number of coloured spheroids and formmg nests ot blood- 

 corpuscles or minute ' blood-islands.' After a time the cells become elongated and pointed at their ends, and 

 processes grow out to join prolongations of neighbouring blood-vessels or of similar cells. _ At the same time 

 vacuoles form within them, and becoming enlarged coalesce to form a cavity filled with fluid, m which the reddish 

 globules, which are now becoming disc-shaped, float. Finally the cavity extends through the cell-processes into 

 those of neighbouring cells, and a vascular network is produced, and this becomes eventually united with pre- 

 existing blood-vessels, so that the blood-corpuscles which have been formed within the cells in the manner described 

 get into the general circulation." ^ 



The " intracellular " mode of development of the red blood-corpuscles in most animals ceases at or before birth. 

 They are supposed to be developed after birth (in the growing child and adult) from the red marrow of the bones, 

 especially that of the ribs, and from the leucocytic marrow-cells called erythroblasts . This view is, however, disputed, 

 and the erythroblasts, according to Bizzozero, are not developed from the leucocytic marrow-cells, nor from the 

 white corpuscles of the blood, but are corpuscles sui generis, which multiply by karyokinesis, and become gradually 

 transformed in the mammaha, with the disappearance of the nucleus, into the red blood discs. 



This view is favoured by Professor Schafer, who states that the coloured cells observed by him " have almost 

 always been distinctly smaller than the ordinary marrow-cells, often of irregular forms, and sometimes appear to 

 be undergoing division. They are amoeboid cells, the protoplasm of which is coloured by haemoglobin, and they 

 closely resemble the nucleated red blood-corpuscles of the embryo. It appears, therefore, probable that the cells 

 in question are descendants of the embryonic red blood-corpuscles, and that they are transformed into the ordinary 

 blood-discs by the gradual atrophy and disappearance of the nucleus and the moulding of the coloured cell-substance 

 into the shape of the bi-concave red corpuscles." It will be observed that the series of changes which result in the 

 formation of blood and blood-vessels are self-inaugurated, and in no way influenced by irritability, external stimuli, 

 or environment. 



The production of young blood is especially interesting in its relation to the capillary blood-vessels ; the blood 

 and the channels through which it is to flow being practically developed at the same time. The simultaneous 

 development is an important feature as indicating design. The blood-vessels and their contents are evidently part 

 of a general scheme. 



Similar arrangements are witnessed in the growth of young bone, which may be developed in membrane or in 

 cartilage. In the flat bones of the head (membranous to begin with), such as the frontal and parietal, the membranes 

 are stiffened by the deposition of lime (earthy salts). This lime is not, however, scattered all over the bones. On 

 the contrary, it radiates from an appointed centre stellate-fashion, and spreads towards the periphery of the bones. 

 In like manner the long bones which have their origin in hyaline cartilage have separate centres of ossification ; the 

 centres increasing according to age until puberty is reached. Thus in the femur or thigh bone, the first centre 

 of ossification appears in the middle of the shaft about the beginning of the third month after impregnation. In 

 this case the ossification extends up and down the shaft before the other centres appear. Towards the end of foetal 

 life a second centre appears at the lower portion of the bone and forms part of the knee-joint. A year after birth, 

 a third centre appears at the upper end of the bone and assists in forming the hip joint. During the fourth year 

 a fourth centre appears and forms the knob known as the trochanter major; a fifth centre appearing during the 

 fourteenth or fifteenth year to form the trochanter minor. The thigh bone is thus developed from five centres (the 

 sacrum has as many as thirty-three centres). The shaft or body of the bone is called the " diaphysis " ; the other 

 parts being designated the " epiphyses." In all this there is marked order and strict adherence to a building plan ; 



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. 



