334 ZOOLOGY. 



come from winter clirysalids, and P. marcdlus from a 

 second brood of summer clirysalids. Merrifield has shown 

 in the case of two European geometrid moths that both 

 the markings and colors were materially affected by the 

 temperature to which the chrysalis was exposed. On the 

 other hand Fenn bred a very long and varied series of 

 Ennomos subjected to the same temperature. lie believed 

 that the presence or absence of moisture, rather than dif- 

 ferences of temperature, was one of the principal causes of 

 variation. Both experimenters, however, ajipear to believe 

 that the variations arose in response to changes in the 

 external conditions of life. 



As the result of subjecting pupas to heat or cold Stand- 

 fuss, in Zurich, has elicited various kinds of effects: 

 1. Seasonal forms similar to those known to occur in 

 nature {Van&saa c: allium and Papilio macliaon to some 

 extent). 2. Local forms aud races similar to those which 

 occur constantly in certain localities (Vaneftsa urticw, 

 cardui, and to some extent P. macliaon and V. anfiopa). 

 3. Entirely exceptional forms or aberrations, also occurring 

 from time to time in nature ( T'. io, cardui, Argynnis 

 aglaia). 4. Pliylogenetic forms, not now existing, "but 

 which may either have existed in past epochs or may 

 perhaps be destined to arise in the future ( F. io, anfiopa, 

 atalanta). 



Food. — While changes of heat and cold, moisture and 

 dryness, are fundamental factors in causing variation, the 

 abundance or scarcity and the nature of food are an equally 

 potent agency not only affecting growth and reproduction, 

 but in jjroducing variation, and by causing a change in 

 habits bringing about profound modifications of the body. 

 We will begin with the simplest organisms. Maupas 

 believes that the reproductive power of ciliate infusoria 

 depends (1) on the quality and quantity of food, (2) on 

 the temperature, and (3) on tlie alimentary adaptation of 

 the buccal organ. "With favorable nutrition an infusorian 

 {Styloiiichia pusiulata) undergoes self-division once in 



