232 Merkel Henry 'Jacobs 



measurements made on several different individuals before and 

 after the addition of v^^ater it was determined that rotifers w^hich 

 had contracted to one-third or one-fourth of their original volume 

 and remained in this condition for several weeks or a month were 

 perfectly capable of being revived. A number of careful measure- 

 ments showed that under all conditions of drying — on a clean shde, 

 with sand, on filter paper, etc. — a very considerable shrinkage 

 occurs, the exact amount being dependent on the conditions of the 

 desiccation. How can such results, which may be obtained by 

 anyone with very little trouble, be reconciled with Davis' theory 

 that loss of water is prevented by an impermeable secretion .^ If 

 the water is retained within the body how can such loss of volume 



occur 



It might be suggested, although such a supposition sounds 

 rather improbable, that loss of water occurs up to a certain point 

 but that by the time this point is reached formation of some sort 

 of a protective covering has gone far enough to prevent its further 

 escape. That a protective covering impermeable to water is not 

 present is shown by the following experiment. Several rotifers 

 were dried for a month under the most favorable conditions pos- 

 sible; at the end of that time they were examined and seen to be 

 considerably shrunken. A small piece of wet filter paper was 

 then placed in the dish in which they were contained in such a 

 way as not to touch them, and the dish was covered with a piece of 

 glass. Camera drawings were made of the rotifers at intervals 

 of one minute to determine the effect of the moist atmosphere. A 

 distinct swelling was observed in one minute and in five minutes 

 the volume had increased perhaps 50 per cent. The dish was 

 then uncovered and shrinkage immediately occurred. When 

 water was added the rotifers recovered normally. This experi- 

 ment, therefore, shows conclusively that in rotifers dried in such a 

 way that recovery is possible after a desiccation lasting for a month 

 the covering of the body is freely permeable to moisture. It is 

 certain, therefore, that no such protection as that demanded by 

 Davis' view is present. 



It might perhaps be objected that in the above experiment the 

 swelling observed took place mainly in the superficial part of the 



