jgoS] JENNINGS— HEREDITY IN PROTOZOA. 417 



constriction until the two halves separate. This lengthening is clearly 

 evident in the figures and in the correlation table giving depth of 

 constriction with length of body (Table XL, page 441). As Table 

 XL shows, there is a period at the beginning, before the constriction 

 reaches a depth of about 10 microns, when there is little relation 

 between the length of the body and depth of constriction, showing 

 that in this period the halves have not yet begun to lengthen. We 

 may therefore take the length of the young at this period as that 

 characteristic for the young individuals in their earliest recognizable 

 condition, before growth has begun. By dealing with these alone 

 we are able to compare the variability of the young with that of 

 the adults, or with random samples including all ages. In the further 

 treatment, therefore, the measurements of the unseparated voung are 

 divided into two classes: (a) those before lengthening has begun; 

 (b) those after lengthening has begun. 



(a) The Unseparated Halves before LengtJiening Has Begun. — 

 .Studies were made of the young of three lots of the eaiidatuni group 

 (descendants of the individual D), and of two lots of the aurelia 

 group (descendants of the individual c). Each "lot" included 

 individuals taken on the same day from the same small culture. In 

 most of the lots there were examined: (i) The unseparated young 

 before growth had begun; (2) the unseparated young after growth 

 had begun; (3) a random sample, including all sorts of individuals 

 found in the culture. The results of these measurements are given 

 in Table A'lIL, page 418. 



(i) The caudatiini Form (Descendants of D). — The most 

 thorough study was made of lot i, of the caitdatitm group; the 

 results there reached are typical, and perhaps more reliable than any 

 others, owing to the large numbers examined. We shall therefore 

 make the results on this lot the basis of our discussion, afterward 

 bringing out points of difference and resemblance shown in the 

 other lots. 



From this lot i, I measured 313 dividing specimens, which, of 

 course, included 626 unseparated young; a random sample of 200 

 individuals not dividing was likewise measured. A correlation table 

 for the 313 dividing specimens, giving the depth of the constriction 

 below the general body surface and the length is given on page 441 



