ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 37 7 



figure 2 18, lays its eggs in the stems of bur-reed and iris, 

 growing in temporary pools. The eggs at first develop 

 rapidly as in other damselflies, and reach the condition 

 shown in figure 219 about the time that these pools nor- 



y 



Fig. 220. Animals that withstand dessication. z and j, a tardigrade 

 {Macrobiotus hufelandi) x, extended, creeping; y, in a state of apparent 

 death, dried; z, a. votiiev (Philodina megalotrocha). Internal organs ot the 

 tardigrade shown in optic section: m, pharynx; n, salivary gland; o, 

 stomach; p, ovary; i, ii, iii, iv, legs of one side, (z and y, after Hertwig, 

 z, after Jennings. 



mally "go dry." There they stop, and in that condition 

 they remain until the rains of autumn refill the pools, 

 when they resume development, hatch out and enter the 

 water. 



There are many lesser organisms, notably the tardigrades 

 and rotifers (fig. 220), so well adjusted to the exigencies of 

 drouth they can get along and maintain themselves, living 



