A WORLD OF BILLIONS 



15 



fact that the dovolopment, as studied 

 in the chick and otlier lower animals 

 and in tlie human nviim and cmlti'vo. 

 follows exactl}' siniihir lines. .Similar 

 organs develop in similar ways. The 

 wliole vertehratc kingdom from the 

 lowest aninuil consisting of only one 

 cell to nuin, follows the same general 

 l)lan although varying in details from 

 animal to animal, and growing more 

 and more complex as we ascend in the 

 scale. 



Ill 



The Wonderful Powers Implicit, 

 i.e. Ixfolded ix the Fer- 

 tilized Ovum 



Having reviewed the enormous num- 

 her of cells in the blood and the body — 

 whether of man or other animals — and 

 their orderly development by differ- 

 entiation in structure and function, it 

 will be of interest to consider the won- 

 derful powers implicit — that is to say, 

 which are infolded— in an ovum. These 

 powers remain latent until fertilization 

 takes place. Then they immediately 

 start up into amazing activity. We can 

 best study it in the development of the 

 chick in the fertilized hen's egg as just 

 indicated. From the moment when the 

 hen begins to sit, hour by hour, there 

 begins and goes on during the whole 

 period of incubation (twenty to twenty- 

 one days) the most marvelous growth 

 and development. Within even the first 

 three days there is developed, in the 

 growth from the one single cell, a mass 

 in which can already be distinguished 

 the front, middle, and hind parts of the 

 brain, the starting points of the eyes 

 and the ears, even the pulsating heart 

 can be seen, divided at first into only 

 two separate halves. There is a begin- 

 ning of the circulation of the blood. 

 What will become the lungs, the liver, 

 and the pancreas are recognizable. 

 Later the fore and hind limbs of quad- 

 rupeds, the wings and legs of birds, or 

 the arms and legs of the human body 

 begin as little buds. The cartilages of 



the ilii:ils (lingers and toes in man) 

 M'oii rolliiu. Foster and Balfour^ say 

 tlial (Ml llic lll'tli day "the embrvo (if 

 a hird does imi mattn-ially diU'er in 

 its eai'ly ]>liases I'l'om that of a reptile 

 or a mammal, even in the points of 

 structure which are most distinctively 

 avian"' (that is, characteristic of birds). 

 By the sixth day the distinction be- 

 comes clear. 



In all this apparent "hurly-bui-ly," as 

 when a cell in the silkworm multiplies 

 itself 500 times each day, or less swiftly 

 in the cases of vertebrates, there is an 

 orderly, almost uniform development 

 of each animal after its kind. 



For a moment let us limit our- 

 selves to the consideration of the liu- 

 man body and ovum. Look at the 

 .symmetrical and asymmetrical organs 

 of the body. We have two ears, two 

 eyes placed always in front and not at 

 the side of the head as in the fly, the 

 horse, and many other animals, always 

 at a certain distance apart, within a 

 very slight maximum and minimum 

 range; two ears, two arms, two legs, 

 two lungs, two kidneys. Even the nose 

 is symmetrical ; but the two nostrils are 

 fused into one central organ. The 

 tongue also is composed of two sym- 

 metrical halves fused together. The 

 bones of the head are as a rule in pairs, 

 right and left, or if in the middle. line, 

 they have originated in two symmetri- 

 cal halves as in the upper jaws (maxil- 

 la) which are not fused together, while 

 in the lower jaw (the mandible) the 

 two halves are permanently united for 

 its special function of biting and crush- 

 ing the food. The ribs, right and left, 

 correspond to one another. The com- 

 plete or ideal vertebra consists of a body 

 and a pair of ribs which are also joined 

 together in front, not directly but indi- 

 rectly, by means of the sternum or 

 breast-bone. In the neck the ribs are 

 suppressed, but have their representa- 

 tives in little processes or knobs of 

 hone. In the loins (the lumbar 



^ Elements of Embruolooy, p. 275. 



