DYNAMICS OF MORPHOGENESIS 109 



were placed in these dishes in the solution and a number of the 

 dishes were placed in larger glass jars. A liter or more of the 

 same solution was then poured over the dishes to seal them and 

 was allowed to remain in the large jar, which was then covered 

 with a glass plate sealed on with vaseline and weighted. Here 

 also all fluids were renewed at least every forty-eight hours. 

 Later still I found that the worms or pieces would live in water 

 in corked liter Erlenmeyer flasks with only a small bubble of air 

 at the top. When the water in the flasks was changed every two 

 to four days and not more than twenty-five or thirty large worms 

 or their equivalent in smaller worms or pieces were introduced the 

 worms could be kept indefinitely under these conditions without 

 any injurious effects and showed as high a rate of metabolism as 

 the animals kept in open dishes. In my later experiments the 

 flasks have been used almost exclusively and have given very sativS- 

 f actory results. Their only disadvantage is the necessity of remov- 

 ing the worms to other dishes for microscopic examination, but this 

 is not serious if Erlenmeyer flasks are used for the animals can be 

 dislodged with no great difficulty and without injury by means of 

 a current from a large rubber bulb pipette. In consequence of 

 the very small surface of the fluid exposed in the neck of the flask 

 the loss of the anesthetic is very slight, even if the cork is not per- 

 fectly tight-fitting. Moreover, except in very low concentrations 

 or after acclimatization to the anesthetic, the animals are usually 

 at the bottom of the flask. It is certain therefore that decrease 

 in concentration as a source of error is eliminated. 



a. Alcohol. Series 71: August 10, 1905. Thirty worms 8 to 

 10 mm. in length and well fed were cut into two pieces, a including 

 the region between the levels 1 and 5 in figure 1, and b, the region 

 from 5 to 8, the posterior end in figure 1. These pieces were 

 placed in 1.5 per cent alcohol at a temperature of about 22°C. 

 4 control series in water was not made in this case since every- 

 one who has worked with Planaria knows that pieces like a and 

 b give under normal conditions practically 100 per cent of normal 

 animals. 



After ten days in alcohol with a renewal of the mixture every 

 forty-eight hours the pieces were examined. As far as they con- 



