BY HEBER A. LONGMAN. 15 



The extraordinary variation in the teeth of vertebrates 

 may also be instanced. Many writers have pointed out 

 the wide range of dental characters to be found in the 

 Marsupialia, obviously illustrating adaptations to diet. 

 Herbert Spencer was apparently the first to remark how 

 plastic A\ere the teeth of domesticated dogs, through use 

 and disuse, and how they had degenerated in the pug-dog. 

 King Charles Spaniel and other indoor dogs.* N. 



Hollister has demonstrated that lions reared in captivity 

 show cranial differences which would be considered of 

 specific value in wild animals. These differences are the 

 result of the non-development of "' gripping, holding, 

 tearing, lilting and shaking "" muscles owing to methods 

 of feeding in captivity. These changes " are thus produced 

 in the life of a single individual within from five to seven 

 years almost as rapidly as if hy • mutation." "f The 

 megadont molars of a negro or of an Austialian Aboriginal, 

 when compared with those of a Eurojiean reared on a 

 comparatively soft diet, are of interest here. The third 

 molar in these lower races is frequently larger than the 

 second and may have five cu!>ps. It is, of course, true 

 that such characters remind us of those of anthropoid apes, 

 and the occasional presence of a fourth molar may be a 

 primitive feature, J accessor j- molars being common in 

 apes. 



Many well-known examples can be quoted with regard 

 to insects. As Prof. W. M. Wheeler points out in his 

 important study of ants, the food of the larva is ' one of 

 the most important of all stimuli." S By feeding larval 

 workers with "" royal jelly. " the period of development in 

 the bee is accelerated and a queen is formed. (Parenthetic- 

 ally, it may be noted that Wheeler criticises in this book 

 Weismann"s views as to the powerful support given to his 

 theories by the prevalence of neuters amongst certain 

 Hymenoptera) . 



The functions of endocrine organs or ductless glands 

 (such as the pituitary body, the pineal gland, the thyroid 



*H. Spencer: Essays, I., 1891, p. 401. 



fN. Hollister: Proc. U.S. Nat. Mus., LIIL, 1917, p. 177. 



JLongman : Mem. Qld. Mus., VI., 1918, p. 4. 



§W. M. Wheeler: Ants, Their Structure etc., 1912 p. 103 



