BIOLOGY 



erate temperature. The water may get a few degrees 

 warmer than they are accustomed to, and may be insuffi- 

 ciently aerated, but there is nothing to alarm them and 

 induce them to make use of their remarkable means of 

 protection (whatever they may be). Exposed to low 

 temperatures or to salt water, they contract into httle 

 round balls, and in this state they are (somehow) safe. 

 In the cold water, which is just shghtly unfavourable, 

 they see no cause for alarm, and so, as Mr. Shackleton 

 aptly expressed it when told about it, " they go out with- 

 out their Burberries," that being the great sin against 

 prudence on the part of a polar explorer. 



The rotifer is not as a rule a long-lived animal. I 

 have heard of a patriach of five months, which then came 

 to an untimely end. Generally their span is to be meas- 

 ured by days or weeks, or at any rate, is limited by a single 

 season. The majority of the creeping rotifers can protect 

 themselves against drying up, by coating themselves with 

 a kind of varnish, and so they prolong what would be an 

 ephemeral existence through a period of years. As all 

 activity is suspended it may be questioned whether the 

 animal gains anything by this marvellous protective 

 capacity, but at least the chances of the race surviving are 

 greatly increased by it. The Antarctic rotifers in like 

 manner exist in a state of suspended animation when 

 frozen in ice for a long period. If the lakes in which they 

 live are only melted at long intervals and for short periods, 

 it may be that some very ancient rotifers are ahve beneath 

 the ice, possibly scores of years old. 



Viviparous Rotifers 



Most rotifers lay eggs, but a good many kinds bring 

 forth the young alive and very completely developed. At 



voi.n.-i6 241 



