APPENDIX A 



The tracing of the details of the development of animal forms 

 from the primitive single cell is a rather complicated process in- 

 volving the use of various technical terms and the names of 

 numerous types of animals which are quite unknown except to 

 specialists in zoology. 



So it has seemed advisable not to incorporate the discussion of 

 eogenesis in the body of this work, but instead to consider this 

 important subject separately in an appendix. 



All animals living at the present time develop from a single 

 cell. As this is true of every animal of which the development is 

 known, we have no hesitation in assuming that it has always been 

 true of every animal type. From this it naturally follows that 

 all types of animal life must be explained in terms of an original 

 single cell. 



Since all types of animal life must be explained and interpreted 

 in terms of a single cell, a path must be traced from the original 

 and primitive single cell to the basic form or forms in every 

 phylum. 



Some animals possess bodies which are composed only of single 

 cells. Such animals are always very small (fig. 87, p. 161). The 

 bodies of other animals are composed of cells belonging to only 

 two germ layers (fig. 117, p. 185), the ectoderm and endoderm. 

 These animals are always radial, or fundamentally radial, in sym- 

 metry, more or less like a flower, and for the most part live firmly 

 fixed to some support and grow after the fashion of a plant. 

 Most of them are of medium size or small, like the sea-anemones 

 or the hydroids, but a few, as certain jellyfishes, may be very 

 large. Those which live, like jellyfishes, suspended freely in the 

 water have only very feeble locomotor powers. 



All creatures living on the land, and a very large proportion 

 of those living in the sea and in fresh water, have their bodies 

 formed of cells derived from three germ layers (fig. ixo, p. 185). 

 Such animals may be small, scarcely more than one one-hundredth 

 of an inch in length, or very large, like elephants and whales, or 

 of any intermediate size. 



It is almost invariably assumed that the animals with bodies 



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