226 PROCEEDINGS OF THE ACADEMY OF [ApHl, 



ual: "(1) Dass das Gemeiusame eiuer grossern Thiergruppe 

 sich friiher im Embryo bildet, als das Besoudere. (2) Aus dem 

 Allgemeinsteu der Fonnverhiiltuisse bildet sich das weniger 

 Allgemeiue uud so fort, bis eudlich das Specialiste auftritt. (3) 

 Jeder Einbryo eiuer bestimmteu Thierfonn, austatt die andereu 

 bestiinmteu Formeu zu durclilaufeu, scheidet sich vielmehr von 

 ihneu. (4) Im Gruude ist also uie der Embryo eiiier hoheru 

 Thierfonn eiuer audereu Thierform gleich, souderu nur seiuem 

 Embryo." He objects to the hypothesis that no adult animal 

 has a yolk sack; that uoue is surrounded by embryonic fluids; 

 that it is not the case that an embryo of a higher animal in 

 each ontogenetic stage corresponds in every point with an advUt 

 individual of a lower species; that it is not the case that in the 

 ontogeny of a lower form structui-al relations do not occur which 

 are found in the adult of a higher form; and that parts which 

 are characteristic of only the highest forms do not appear latest 

 in the ontogeny. He recognizes that there are indeed many cor- 

 respondences between ontogenetic stages of higher and adult 

 stages of lower forms, but contends that it is " noch nicht erwei- 

 sen, dass jeder Embrvo eiuer hoheru Thierform allmahlig die uie- 

 deren Thierformeu durchliiufe, vielmehr scheint sich der T}^us 

 jedes Thiers gleich anfangs im Embryo zu fixiren und die ganze 

 Entwickelung zu beherrscheu." Any one who reads carefully 

 this classic work will find there staled, very acutely and logically, 

 most of the objections, generally supposed to be of much more 

 modern dale, to the theory. 



Fritz Miiller" held that the theory is in the main correct, but 

 pointed out that phylogenetic traces may become more or less 

 obliterated in the ontogeny; he held, accordingly, thai the lack of 

 exact correspondence is due to embryos adapting themselves to new 

 modes of life. Haeckel has develojied the theory most thoroughly; 

 and has consequently used it most in the determination of phylog- 

 enies. He terms the theory the " biogenetisches Grundgesetz, " 

 and states it: " Die Ontogenie (Keimesgeschichte) ist eine kurze 

 Wiederholung der Phylogeuie (Stammesgeschichte)." He also in- 

 troduced the terms ' ' palingenesis ' ' and ' ' cenogenesis, ' ' and states : 

 "Die Phylogenesis ist die mechanische Ursache der Ontogenesis." 

 Thus Haeckel' s position in regard to this hypothesis is in some 



2« Fur Darwin, 18t)4. 



