INFLUENCE OF INBREEDING ON HYDATINA SENTA. 3 



recorded, of which there were a few, were not included in this 

 computation. 



2. Size of family of fertilized sexual females. It appears that 

 the male does not appreciably affect the number of eggs laid by. 

 the female with which he is mated. The size of family is deter- 

 mined almost wholly by the female herself. In -determining 

 size of family in this case, I have counted the eggs laid, not the 

 number that hatch, as experiments have led me to conclude that 

 the vigor of the parent is responsible for the number of eggs, but 

 not for their viability. 



3. Number of eggs laid per day. The young rotifers were 

 isolated and recorded about the same time each day. To find 

 the average number of eggs per day in a given line, the total 

 number of offspring hatched by that line was divided by the 

 number of days on which they were produced, the days for each 

 family being counted separately. Each family was produced 

 usually in three to five days. In a line comprising nine genera- 

 tions, therefore, the number of days as used in this computation 

 would be 27 to 45, regardless of the fact that several families 

 were producing young at the same time, and that the experiment 

 covered only about 20 days. The first day and the last day on 

 which a given female produced daughters were counted as half 

 days, which they must have been on the average, since the 

 offspring recorded as of one such day must have been in some 

 cases the output of a few hours, in other cases of practically a 

 whole day. It is assumed that the eggs hatched in fairly uniform 

 time, as observations have shown that they do. 



4. Number of days required to reach maturity. By this is 

 meant the interval between the laying of an egg and the time 

 when the female that hatches from it begins to lay eggs. This 

 time varies considerably in different lines even when reared under 

 identical conditions. It has been found in some cases that in one 

 line that has passed through over ninety generations partheno- 

 genetically, about three days are required to reach maturity, 

 while a young and vigorous line reared at the same time required 

 less than two days. In the present experiments the time required 

 to reach maturity is an average of the parents of all the genera- 

 tions in a given line. It is the interval between the hatching 

 of the first daughter of the first generation and the hatching of 



