Royal Microscopical Society. 207 



Tardigrades ; individuals of which have been kept in a vacuum, 

 with sulphuric acid and chloride of calcium (thus suffering the 

 most complete desiccation that the chemist can effect), and yet have 



not lost their capability of revivification their return to a 



state of active life, after a desiccation of unlimited duration, may 

 take place whenever they meet with moisture, warmth, and food." 



All the modern scientific works tell the same tale ; a dry rotifer 

 must be the driest thing in existence ; but privately and out of 

 book several good observers have expressed their doubts. They 

 cannot believe that the rotifers are completely dried, and yet they 

 cannot explain away the undoubted drying effects of an oven at 

 200° (Fahr.), or of the vacuum of an air-pump. The only modern 

 writer I can find bold enough to put his doubts into print is to be 

 read in the first volume of the ' Cornhill Magazine.' He cleverly 

 attacks the "dry" subject, shows that when separated from sand 

 or dirt the rotifers die in drying ; concludes that sand and dirt some- 

 how keep moisture in them under trying circumstances, and thinks 

 there have been "mistakes somewhere" about the air-pumps and 

 ovens. 



My experiments at first were merely repetitions of those of the 

 old observers, and the results were nearly the same. The rotifers 

 could be heated gradually up to 200° (Fahr.) in an oven, and some 

 revived with water afterwards : with thermometer standing at 300° 

 two hours' baking completely cooked and killed them all ; so did 

 boiling for three hours ; but most of the experiments were made with 

 a modern air-pump of the best construction. Two large vessels 

 of strong sulphuric acid were put into the receiver, and a dry tank 

 containing P. roseola in great numbers. The receiver was ex- 

 hausted to the utmost, and so kept for a week. Then the tank 

 was removed and moistened ; about a dozen rotifers crawled feebly 

 out, and two or three put forth their rotatory disks : they all died 

 in a few days. 



Now we are taught that this experiment is conclusive, the dozen 

 rotifers having suffered " the most complete desiccation the chemist 

 can effect," must needs have been dry. By no means. According to 

 my belief, the few rotifers revived because they were not desiccated, 

 in spite of the effective chemist, while the scores of non-revivers had 

 been dried, partially or entirely, and killed ! 



Then, how are rotifers protected against desiccation? The 

 philodines constantly give off a slimy secretion ; in drying they 

 contract head and foot-tail (Fig. 3), and as they gradually assume 

 an ovoid form (Fig. 4), the gelatinous fluid dries over them into 

 a hard thin shell, and effectually secures them from even " the most 

 complete desiccation the chemist can effect." 



And now for proofs : as evidence that they really have such a 

 secretion, I merely quote one witness of many, a valued corre- 



