98 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 
the 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 his 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 
appreciated: strange that it should be so,—for, 
had his countrymen recognized his genius, they 
might have earlier claimed him as the commen 
uf the great French naturalist. 
Baer also founded the science of Embryology, 
under the guidance of his teacher, Ddéllinger. 
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 
lifferently from the Articulate, — the Articulate 
