1 78 Heredity. 



which propagate by alternate generation, the process is this : an 

 ovum produces a simple organism, and this propagates by gem- 

 mation ; the creatures thus produced resemble neither the parent 

 nor the original organism ; next the primitive type reappears, and 

 with it the attributes of the two sexes, and propagation by ova. 

 Thus, in the medusa, between two perfect types we find three, as 

 follows : 



ist generation Medusa Great-grandfather 



2nd Ciliated larva Grandfather 



3rd Polyp Father 



4th Strobila Son 



5th Medusa Great-grandson 



It is not here, as in cases of metamorphoses, the same in- 

 dividual which passes from the larval to the nymph state, and then 

 becomes a perfect adult : here we have several individuals totally 

 different from one another. 



The conclusion to be drawn from these facts is, that we 

 ordinarily understand heredity in too narrow a sense, looking 

 at it only under its immediate form from one generation to the 

 next. But, as we see, it may embrace a much larger cycle. It is 

 true that these phenomena are met with only in the lower species, 

 and there are no instances of alternate generation among verte- 

 brates : but still they show how strong, tenacious, and, so to speak, 

 unlimited is heredity. At the same time it gives us a better under- 

 standing of atavism. The two facts, indeed, are not identical, and 

 we do not at all mean to say that atavism is a form of alternate 

 generation, yet the mind readily perceives an analogy between 

 them. Reversional heredity in man seems less singular to us 

 when we compare it with these orderly cycles ; and on witnessing 

 these indisputable facts we can better understand how great is the 

 force of heredity. 



At a time when alternate generation was yet unknown, Burdach 

 and Girou de Buzareingues were led by their researches to admit 

 that there are stronger resemblances between grandfather and grand- 

 son, grandmother and granddaughter, than between father and son, 

 mother and daughter. This is expressed in the following table. 

 (Burdach, Physiologic, ii. 269) : 



