2 1 2 THE BEGINNINGS OF LIFE. 



occurring with a still more mysterious regularity 

 there is gradually evolved the future organism, however 

 complex J . 



Hitherto we have considered the mode of origin of 

 spores, germs, and ova, but if we turn our attention 



period when the development of the embryo begins to manifest itself. 

 But in the higher animals, at least, the weight of evidence appears to me 

 in favour of the view that the process of segmentation results directly 

 in the formation of blastodermic cells. The facts now established by 

 the observations of Reichert in Entozoa, in 1841, of Ransome in osseous 

 fishes, and more particularly those of Remak in Batrachia, that a deli- 

 cate membrane is formed over the surface of each of the segments as 

 they appear, and that the last and smallest segments possess a delicate 

 membranous envelope, appear to show that, in these animals, each seg- 

 ment has the structure of an organized cell, and is very similar to, if not 

 identical with, those of the blastodermic lamina.' 



We shall find, hereafter, that the mode of production of cells described 

 by Bischoff as occurring during the development of the ova of the 

 guinea-pig and of the deer, can be almost exactly paralleled by a similar 

 production of cells, in certain areas of the ' pellicle' which forms on organic 

 solutions. In these cases, also, the material that undergoes change is 

 an albuminous basis substance, containing a multitude of newly pro- 

 duced granules (plastide particles and bacteria). 



1 It is interesting to note the very large proportion of fatty com- 

 pounds which enter into the composition of the yolk of eggs, and also, 

 as previously stated (note, p. 178), in the reproductive cells of many 

 algae. Many of these fatty products seem to be extremely unstable, and 

 therefore well suited to initiate developmental changes. It is in the 

 ovum especially, and in nerve tissue, that complex phosphuretted fats 

 are met with and it is here also that developmental and metabolic 

 changes occur to the most notable extent. According to Dr. Allen 

 Thomson, in the egg of the common fowl ' the yolk contains little 

 more than half its weight of water, or 54 per cent. The remaining 

 46 parts consist of about 17 of albumen, or analogous principles, 28 

 of oily matter, and 1^ of salts. These last are chiefly alkaline muriates 

 and sulphates, phosphate of lime and magnesia, and traces of iron, 

 sulphur, and phosphorus.' (Loc. cit. p. 61.) 



