DESICCATION IN PHILODINA ROSEOLA. 347 



Desert Laboratory at Tucson, Ariz., describes cytological changes 

 accompanying desiccation and subsequent recovery in the cells 

 of Echinocactus wislizeni. These two papers, as far as is known 

 to the author, comprise the literature on the cytology of desic- 

 cation. 



Although this paper deals with the same kind of material as 

 was used by Jacobs and although some of the questions asked 

 by him are of most interest here, the problem has been attacked 

 from an entirely different angle and by cytological methods 

 confirms and adds to the results of Jacobs which were obtained 

 by physiological methods. 



The purpose of this study is, therefore, to attempt by means 

 of cytological examination to determine (i) the condition of the 

 tissues of the dried rotifer; (2) the presence or absence of a pro- 

 tecting membrane in the dried condition; (3) the condition of 

 metabolic activity in the tissues of the dried animal and (4) the 

 changes attending a recovery from desiccation. In order to 

 do this it will be necessary to compare carefully the cytological 

 appearance of sections of animals in a condition of dryness and 

 those of animals recovering from desiccation with sections of the 

 normal, active animal. From the data so- gathered the con- 

 clusions will be drawn. 



II. MATERIAL AND METHODS. 



Philodina roseola is one of the common rotifers belonging to the 

 order Bdelloideae. It occurs throughout the world and is found 

 in depressions in rocks, eave troughs or almost any place which 

 is moist or periodically moist and dry. It is usually associated 

 with the unicellular alga, SpJmrella lacustris. Frequently one 

 notices small individuals in hay infusions. These are, no doubt, 

 introduced when dry hay is added to old cultures. Sometimes 

 in infusions rotifers are found which are fully as large as those 

 associated with the alga before mentioned. These may be 

 encouraged to multiply if very weak hay infusion is added from 

 time to time. The weak infusion allows sufficient bacteria to 

 develop to replace the algae as food and it seems not to harm the 

 animals. 



As has been stated by other authors, the behavior of P. roseola 

 is dependent upon a number of factors, chief of which seem to 



