422 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



young of row 4 individuals older (constriction deeper) than in those 

 of row I. 



From a third lot of descendants of D, 154 halves were obtained; 

 in 84 of these the constriction was less than one fourth the breadth. 

 Unfortunately no random sample of this culture was preserved. 

 But 300 individuals just twenty- four hours old were taken from it 

 for other purposes, and the young halves may be compared with 

 these (rows 7 and 8, Table VIII.).* It should be noted, however, 

 that the adults of row 8 had been kept for twenty-four hours in a 

 rather small quantity of water, where food was relatively scarce, so 

 that they were smaller than would have been the case if they had 

 lived throughout under the same conditions as the dividing specimens. 



In general, the same relations are shown here as in the other 

 lots. A striking peculiarity is the great breadth of the young halves 

 (65.716 microns), as compared with that of the adults (40.320 

 microns), so that the ratio of breadth to length (the " mean index ") 

 is more than three times as great in the young as in the adults 

 (78.563 per cent, in the former, 23.899 per cent, in the latter). 

 Owing to the inclusion of older halves, in which lengthening has 

 begun, the correlation between length and breadth is again low 

 (.221 5 ±.0999). 



(2) The onrelia Form (Descendants of c). — Two lots of divid- 

 ing specimens of the aurclia form were examined, the first including 

 132 halves in which lengthening had hardly begun, the second 76. 

 The constants for these, in comparison with random samples of 

 those not dividing, are given in rows 9 to 14 of Table VIII. These 

 show the same relations that we have already seen in the caudatum 

 group, with one exception. In the smaller collection (lot 5), the 

 mean breadth of the halves was a little less, instead of greater, than 

 thai of the random sample. In this culture the animals were extra- 

 ordinarily broad, the mean ratio of breadth to length in the random 

 sample being 41.455 per cent., in place of the usual ratio of about 30 

 per cent. This was due to the fact that these animals had been 

 placed twenty-four hours before in a rich nutrient solution and had 



* The dimensions of the entire dividing specimens of which row 7 are 

 the halves are given in Table XLIV. of the Appendix ; the dimensions of the 

 300 just twenty-four hours old are given in Taljle XLI. 



