ß30 ^'^ HANS GADOW, 



Teratological cases, like repeatedly occurring supernumerary toes, 

 should be excluded, because we are unable to explain liow they were 

 acquired. Cases of mutilation are not likely to be inherited unless 

 the whole organism has been affected througii correlation of a series 

 of changes, wliicb have been necessitated by the regaining of the 

 equilibrium upset by the primary cause or insult. I have therefore 

 tried to select such cases in which the obviously primary modification 

 seems to have brought about changes in other organs ; in other words 

 cases, in which the whole organism seems to have become imbued 

 with the subsequent effects of the original „eingreifende" Modification. 

 Lastly, if these modifications are referable to mechanical strain, they 

 enhance our chances of an explanation, and are less likely to be 

 looked upon as gratuitous Variation s. 



I do not flatter myself that the explanations of the primary causes 

 of the six or seven cases, which I propose to discuss in the following 

 pages, are absolutely binding, on the contrary, I have sometimes sug- 

 gested opposite Solutions and have had to content myself with pointing 

 out which of the two seems to be the more probable. These attempts 

 occasionally necessitated the discussion of, at first sight, rather remote 

 analogies. At any rate the facts are well ascertained; the original 

 specimens figured in the accompanying plates are with few exceptions 

 in the Cambridge Museum of Zoology and Comparative Anatomy. 



The following organs are treated in this essay: 



1. The beak of the Crossbills, p. 630. 



2. The bill of the Wry-billed Plover, p. 633. 



3. The tracheal labyrinth of the Ducks, p. 635. 



4. The tracheal pouch of the Emu, p. 636. 



5. The larynx and the manubrium sterni of Howling Mon- 

 keys, p. 639. 



6. The stomach of the Ostrich, p. 641. 



7. The stomach of the Petrels, p. 644. 



1. The beak of the Crossbills. 



The peculiar formation of the beak of the Crossbills is well 

 known and has attracted the attention of several zoologists ^). The 



individus qui en proviennent, j)ourvu que les changements acquis soient 

 communs aux deux sexes. ou h ceiix qui ont prodiiit ces nouveaux in- 

 dividus. 



1) R. TowNSON „Tracts and Observations in Natural History and 

 Physiology", London 1799, p. 116—123. 



