1891.] MICROSCOPICAL JOURNAL. 109 



Heredity: Its Part in Organic Evolution. 



By Prof. HENRY L. OSBORN, 



HAMLINE, MINN. 



By heredity is meant the transmission to its offspring by a parent of 

 the power to grow into the parental image. Of the fact of heredity in 

 some sense of the word there can be no doubt whatever. It is easy 

 enough to demonstrate beyond any dispute that young animals grow into 

 the likeness of their parents in virtue of the operation of some internal 

 force which guides them in that direction. Thus, for example, the 

 eggs of two species of Echinoderms will develop in tlie same glass of 

 sea water where the surrounding influences, external to themselves, 

 must be the same for each, and yet each follows with unerring step a 

 predetermined path. Eggs of our domesticated fowls can be placed 

 under the same conditions, as in an artificial incubator, or entrusted to 

 that wonderful instinct resident in the natural incubator, but their simil- 

 itude of environment does not turn the embryos aside from their pre- 

 destined course. I have lately been watching the eggs of the salamander, 

 and they are such delicate and helpless things that one would hardly 

 think such feeble folk could be so true, and yet day by day they follow 

 courses exactly similar to those gone through in their growth bv similar 

 or identical European forms and recorded by Von Baer as long ago as 

 1834. Such facts as these show that the environment does not produce 

 the mature animal, but that the egg from its start contains a force which 

 propels it in a definite direction and which we call heredity. The fact 

 that a delicate bit of protoplasm, the egg-cell, can hold its own among 

 the contending forces in whose focus it is placed is the greatest miracle 

 of nature. 



But we must carefully remember that when we have referred the re- 

 semblance of a child to its parent to heredity as its cause that we have 

 not really answered any question regarding the vera causa of the re- 

 semblance, for we have onl}' given the inquirer a word, a name, and 

 not anything more. Heredity, in fact, is one of the fundamental prop- 

 erties of protoplasm which no one has as yet succeeded in reducing to 

 simpler terms. We say, if we use the language of Professor Huxley, 

 that living things are unique among other things in undergoing " cy- 

 clical changes." Having noted what we mean by heredity, we must 

 note in the second place that animals at large present grades of resem- 

 blance less close perhaps than that customarily observed between parent 

 and offspring, and yet a structural resemblance which has not escaped 

 observers from a very early date in the history of nature-study. Attempts 

 at classification of animals or plants 'are based upon these resemblances. 

 At first the c[uestion into the meaning of these resemblances was not 

 thought of, but later it arose and has been answered in only two ways. 

 By one school of philosopical biologists the resemblances were under- 

 stood as indications that the animals were as one might not irreverently 

 say made to order, and made by varying a few patterns a little this way 

 or that. This conception was that which Prof. Louis Agassiz ably de- 

 fended in his Essay on Classification. Its failure to account for many 

 of the facts of embryology and comparative anatomy led it to be re- 

 jected by most biologists. By the other school of biologists the resem- 

 blances were understood to indicate more or less remote actual genetic 



