336 ZOOLOGY. 



Barfiitli sliows tliat wliile low temperature retards the 

 growtli and metamorphosis of tadpoles, quiet and fasting 

 also curtail them. Fasting is an es])ecial]y important 

 factor in shortening the last stages of metamorphosis. In 

 other cases fasting plays an important role in development. 



The Japanese produce sti-ange, grotesque varieties in gold- 

 fish through the action of selection, confinement in tanks 

 or aquaria, with comparativclv limited room for swimming, 

 plenty of food, etc.; and Dr. Walil in six years intensified 

 these results by developing enormous and abnormally 

 lengthened pectoral, ventral, dorsal, double anal, and 

 caudal fins in his stock. Eyder reported that some of the 

 races of these fish had obviously been affected in appear- 

 ance by abundant feeding, as was attested by their short, 

 almost globular bodies, protuberant abdomens, and greedy 

 habits. Darwin also refers to the great variability in fishes 

 reared in the great tanks of India. 



On the other hand in animals living in dark caves 

 where the supply of food is scanty the body and appendages 

 become more or less attenuated. 



The experiments of Diising with sheep leave little doubt 

 that abundant moisture and food tend to the production of 

 females, while high temperr^ture iiroduces males. The 

 heavier well-fed ewes produced ewes, while the lighter 

 underfed ewes brought forth males. Girou divided a 

 flock of 300 ewes into two equal parts, of which one half 

 were extremely well fed and served by two young rams, 

 while the others were served by two mature rams and kept 

 poorly fed. The proportion of ewe landjs was GO per cent 

 and 40 per cent. 



Influence of Mechanical Strains and Stresses — Dynamical 

 Evolution. — The hard supports or skeletons of animals 

 gradually arise in the young animal by the deposition of 

 lime, or in certain forms (sponges and radiolarians) of 

 silica, and throughout life the form of the bones, etc., is 

 due to the action of the muscles. Cope remarks: "Mus- 

 cular tissue is highly plastic, and as it is directly under 



