1902.] NATURAL SCIENCES OF PHILADELPHIA, 227 



respects a return to the opinion that was dominant before the time 

 of von Baer. 



Hatschek" gives a brief but able consideration of this hypothesis : 

 " Die Ergebnisse der vergleichenden Ontogenie habeu stets nur den 

 Werth von AVahrscheinlichkeitssehliisseu, genau in demselben Grade 

 wie die der vergleichenden Anatomic. Die relative Sicherheit hangt 

 in beideu Fallen nur von der Meuge der Praemissen uud von der 



Scharfe des Schliessens ab Die INIethode der vergleichenden 



Ontogenie ist eine Erweiterung der vergleicheud anatomischen 

 Methode (Festelluug von Homologie uud Analogic) durch An wen- 

 dung derselben auf Formeureihen Da der iudividuelle 



Organismus nicht durch einen einzigen Formzustand, sondern durch 

 eine Formenreihe repriisentirt ist, die er wiihreud seines iudividu- 

 ellen Lebens durchliiuft, so kaun es auch nicht geniigeu, allein die 

 Endformeu zu vergleichen, sondern es mass die ganze Formenreihe 

 beriicksichtigt werden. ' ' He concludes also that when a larval or 

 embryonic form is characteristic for a large group, we are only 

 justified in concluding that the ancestor of such a group possessed 

 also this larval or embryonic form ; and only when the latter shows 

 great corresi^ondence with the adult stages of lower forms can it be 

 said with great probability to correspond 1o a similar ancestral 

 form. 



As the biogenetic law is generally held to-day, it assumes that 

 Ihe stages of the individual do not repeat but only to greater or 

 lesser degree parallel the stages of the race : the correspondence is 

 not one of repetition but of parallelism. And in each particiUar 

 case the palingenesis must be distinguished from the ceuogenesis. 

 The possibility of error is in proportion to the difficulty of making 

 this distinction. 



(b) On the Application of this Hypothesis. 



On the principle that the organization should be considered as a 

 whole, there is no d priori reason for disregarding the various stages 

 of the organization. With von Baer we may say that the indi- 

 vidual development consists in a progress from the more general to 

 the more special, and the further the individual of one race de- 

 velops the more it diverges accordingly from individuals of other 

 races. The biogenetic law is an assumption, and put into practice 



" Lehrbuch der Zoologie, 1888. 



