Effects of Desiccation on the Rotifer 243 



greater mortality than those dried slowly in a partially covered dish 

 at the same temperature although in spite of the rapidity with which 

 they were dried they were much less injured than those dried at 20°. 

 We may conclude, therefore, that while rapidity of desiccation is a 

 very important factor in determining the mortality, it is not the 

 only one and it may even be obscured by certain others such as the 

 one mentioned. 



Attention must be called to the extremely high percentage of 

 recoveries and the rapid appearance of movements in the case of 

 the rotifers dried slowly at the high temperature. Although no 

 sand or other solid matter was present and although the drying 

 lasted for four days, fifty-four out of the fifty-seven rotifers 

 recovered normally. This is as high a percentage as is usually 

 obtained under natural conditions. When we recollect that 

 almost all workers on the subject have failed to get any cases of 

 recovery after even a few hours' drying in the absence of sand and 

 that Doyere who is almost alone in having observed such recov- 

 ery admits that in his experiments the mortality was always great 

 and recovery very slow, we see the great importance of the external 

 conditions under which desiccation occurs. 



It is difficult to say just why the high temperature should have 

 a beneficial efi^ect. It cannot be that by promoting chemical 

 changes it causes the formation of a protective secretion since roti- 

 fers dried at the high temperature appear even more shrunken 

 than those dried at a low one and furthermore because they swell 

 with equal readiness in a moist atmosphere showing the perfect 

 permeability of their cuticle to water vapor. Perhaps the high 

 temperature by favoring greater muscular activity may cause a 

 greater contraction at the time of drying and thus prevent the 

 injurious stresses set up in the tissues of a partially extended animal 

 when the water leaves it rapidly. However this may be, it is inter- 

 esting to note that under natural conditions the water in the urns 

 in which Philodina lives must frequently reach a fairly high tem- 

 perature at the time of its evaporation from exposure to the sun's 

 rays and perhaps the greater resistance shown by this rotifer when 

 dried at a high temperature is due to an adaptation to the condi- 

 tions under which it lives in nature. 



