392 LOUIS MAX HICKERNELL. 



are not to be easily compared, yet the initial stimulus is similar 

 and development is the result in both cases. 



Desiccation Phenomena in Their Relation to the Subject of 



Adaptation. 



That desiccation is but one of the unfavorable conditions to 

 which rotifers may adapt themselves is evident from the litera- 

 ture. The Bdelloideae can easily adapt themselves in other 

 ways. Murray in his account of rotifer fauna observed during 

 the first Shackleton south polar expedition found that Callidina 

 constricta and Adineta grandis, both Bdelloids, were able to live 

 for rather long periods in salt water although normally they 

 are found only in fresh water. Murray in the account of his 

 experiments says: 'To test the degrees of cold which they 

 could stand blocks of ice were cut from the lakes and exposed to 

 the air in the coldest weather of the whole winter. By boring 

 into the center of the blocks we found that they were as cold 

 as the air. A temperature of - 40 F. did not kill the animals. 



"Then they were alternately frozen and thawed weekly for a 

 long period and took no harm. They were dried and frozen 

 and thawed and moistened and still they lived. At last they were 

 dried and the bottle containing them was immersed in boiling 

 water, which was allowed to cool gradually and still a great 

 many survived. Again they were put into sea water and into 

 the brine from the bottom of Green Lake which is so salt that 

 it only freezes at about o F. They were kept in these salt 

 waters for a month, yet as soon as they were transferred to fresh 

 water they began to crawl about as though nothing had happened. 



" Such is the vitality of these little animals that they can endure 

 being taken from ice at a minus temperature, thawed, dried and 

 subjected to a temperature not very far short of the boiling 

 point, all within a few hours (a range of more than 200 F.)." 



It is desirable that the structural changes, if any, which ac- 

 company freezing and salinity of the surrounding medium be 

 worked out in order to compare the resulting conditions with 

 those in the dried animals. It is probable that when the different 

 environmental conditions were brought about successively in 

 varying combinations, the structural response is somewhat 

 different in each case. 



