LIFE-HISTORY OF ROTIFER 229 



Thus, under conditions of constant temperature and food, the 

 average length of life is lower than the average for individuals 

 kept under conditions of constant food supply and fluctuating 

 temperature. 



As all these records were from isolated individuals, in many of 

 the cases the short life of an individual may have been due to a 

 slight mechanical injury inflicted when the organism was trans- 

 ferred from one depression slide to another in the daily routine; 

 this is particularly likely to occur towards the close of the life- 

 cycle when the posterior part of the body has become inflated 

 and lost the power of movement. 



When the egg is deposited in the water there is no indication 

 of movement in the embryo; but six to eight hours before hatch- 

 ing the embryo is clearly distinguishable and can be observed as 

 it turns within the egg; the jaws are in constant motion, striking 

 out against the membrane apparently in an attempt to force a 

 place of exit. Just before the individual emerges the egg mem- 

 brane bulges outward near the larger end of the egg and im- 

 mediately over the jaws of the embryo; this bulge increases 

 until the membrane ruptures, leaving an irregular opening 

 through which the organism escapes. The first definite bulging 

 of the egg membrane occurs about two minutes before the 

 organism escapes into the water. After emerging, the young 

 individual moves rapidly, at random, through the water, twisting 

 and bending sharply in its course. The body increases gradually 

 in length and diameter for the first four days. At this time the 

 maximum length is reached in most cases, but the increase in 

 diameter continues until a day or two before death. 



At room temperature the organism begins to deposit eggs 

 about twenty-four hours after it has hatched, and one to two 

 days before the maximum length of the body is attained. At 

 this time a yellow-brown substance begins to appear in the 

 posterior three-quarters of the body; this substance increases in 

 amount until the body becomes brownish in color, the posterior 

 part becomes inflated, and most of the power of movement is 

 lost, owing to the increase in size and the loss of flexibility. In 

 isolated individuals random movement ceases about the second 



