14 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Tic ins. — Do twins occur merely as sports to increase 

 the gaiety of nations ? Or are they extreme examples 

 of a fertility that, occurring in a lesser degree, produces 

 double monsters ? Or, again, does their occurrence 

 associate man phylogenetically with any group in which 

 a pair of young is the normal occurrence ? 



Vigour or Decline. — The female elephant, in certain 

 of its organs — the anthropoid apes, in certain characters of 

 the skeleton, exhibit extraordinary and striking varia- 

 tions. Do such conditions illustrate a progressive ten- 

 dency, or a tendency towards degeneration and decline ? 

 They may be due to a restlessness of disposition caused 

 by excessive vigour, or a nickering vitality, a lack of 

 proper direction and correlation of the forces responsible 

 for the growth of the organism. 



The Significance of Variations. — The share of 

 variations in determining the relationships of species, 

 in deciding the avenue of evolution of an organ or an 

 individual, in even fixing the path of development 

 of an organ in a single species, is, in my opinion, of 

 comparatively small account. Variations per se appear to 

 me to have no more power in the production of specific 

 alterations than the waves beating on the shore in grind- 

 ing corn. 



Excessive development (e.g., double thumb) is not 

 necessarily an advance in development, and vice versa. 

 The variation j^i'oduced may be something quite remote 

 from the disturbance in development which causes it (e.g., 

 Meckel's diverticulum). One variation (e.g., supracondy- 

 loid process) may be of little account to the individual ; 

 another (e.g., patent foramen ovale) is of profound 

 imr)ortanee. A given variation may be common in one 

 species, rare in another (e.g., lateral alterations in the 

 attachment of the ilium and sacrum). 



