28 NOMENCLATURE 



know, when he first proposed his classification, 

 that in its first formation the germ of the Verte- 

 brate divides in two folds ; one turning up above 

 me backbone, to form and enclose all the sensitive 

 organs, — the spinal marrow, the organs of sense, 

 ail those organs by which life is expressed ; the 

 other turning down below the backbone, and en- 

 closing all those organs by which life is main- 

 tained, — the organs of digestion, of respiration, 

 of circulation, of reproduction, etc. So there is in 

 this type not only an equal division of parts on 

 either side, but also a division above and below, 

 making thus a double symmetry in the plan, ex- 

 pressed by Baer in the name he gave it. Baer 

 was perfectly original in his conception of these 

 four types, for bis paper was published in the very 

 same year with that of Cuvier. But even in Ger- 

 many, his native land, his ideas were not fully 

 ireciated: strange that it should be so, — for, 

 bad his countrymen recognized his genius, they 

 might have earlier claimed him as the compeer 

 of the great French naturalist. 



Baer also founded the science of Embryology, 

 under the guidance of his teacher, Dollinger. 

 His researches in this direction showed him that 

 animals were not only built on four plans, but 

 that they grew according to four- modes of devel- 

 opment. The Vertebrate arises from the egg 

 iifferentlv from the Articulate, — the Articulate 



