46 



Aquatic liitz 



what degree? Does the balance estab- 

 lished during the day essentially last 

 over through the night? Do the plants 

 give off so much oxygen in the light and 

 themselves utilize so little during the 

 night that their influence is after all es- 

 sentially the one ascribed to them in 

 the accepted theory of the balanced 

 aquarium ? 



This question is at once of practical 

 and theoretical interest. The writer has 

 asked a number of botanists for infor- 

 mation. What is the condition of the 

 water, say of an aquarium in which there 

 is no animal life, but in which the maxi- 

 mum bulk of a given plant is growing, 

 for instance, after so many hours of 

 sunlight, followed by so many hours of 

 darkness? Is the period of oxygeniza- 

 tion actually followed by one of deoxy- 

 genation, or, as indicated above, is the 

 deoxygenating influence slight as com- 

 pared with the other? So far, the bot- 

 anists to which the writer has appealed 

 have been unable to give answers to these 

 questions, or to point to any literature 

 touching upon them. The writer would 

 be greatly pleased if some reader of 

 Aquatic Life might do better. 



Now for the experiment. Several 

 years ago the writer was engaged in a 

 series of experiments in regard to the 

 metamorphosis of the Tiger Salamander. 

 This animal, of course, lives in the water 

 in its early or tadpole stage. During this 

 period it has a fine system of external 

 gills. It has lungs also, however, even 

 before it hatches from the egg, and at 

 some period in its life its gills are usual- 

 ly absorbed and the animal becomes 

 chiefly an air breather and chiefly a land 

 animal. 



The points at issue, which lead to the 

 experiment, were the following. Could 

 the larval salamander really develop for 

 a long period by the use of its gills alone, 



and at what time would it begin to rise 

 to the surface and breathe by means of 

 its lungs ? 



Two young salamanders were chosen 

 for the experiment. They were about 

 three centimeters long and had hatched 

 from eggs in a large battery jar used as 

 an aquarium. It was situated in an east 

 window and contained a fairly copious 

 growth of several algae. There were 

 small worms and crustaceans also pres- 

 ent which served as food for the two 

 larva. These little animals throve ex- 

 ceedingly, growing as fast as did others 

 in an adjacent pond. They were the pic- 

 ture of contentment, striding about the 

 bottom of the jar with slow searching 

 movements, now and then jabbing and 

 munch, munch, munching if the jab 

 proved successful in approved youn^ 

 salamandrine fashion. Their gills were 

 finely developed. Blood could plainly be 

 seen circulating in them. 



These animals were watched for hours 

 during several days to ascertain wheth- 

 er they rose to the surface for air. But 

 no suggestion of a rising movement was 

 observed. They were plainly living un- 

 der ideal conditions of a balanced aquar- 

 ium. The oxygen that they were absorb- 

 ing through skin and gills was sufficient 

 for their respiratory needs. 



The next question, however, was, 

 what of the conduct of these animals 

 during the night ? Observed by lamp 

 light during the evening they were as 

 quiet as usual. It really seemed to the 

 writer that they were living an exclusive- 

 ly under water life. To prove this, how- 

 ever, a screen of mosquito netting was 

 stretched across the jar about two centi- 

 meters below the surface and held there 

 by means of a light elastic spring. The 

 placing of it was done without exciting 

 the animals. They seemed as content 

 afterwards as before. Yet, to the writ- 



