igoS.J 



JENNINGS— HEREDITY IN PROTOZOA. 



423 



become very plump. The point of interest is that the breadth of the 

 young individuals in the earliest stages tends toward a constant 

 dimension, becoming greater when the adults are thin, less when the 

 adults are plump. Outlines of dividing specimens, and of those not 

 dividing, from this culture, are shown in Fig. 3, o to /; the great 

 difference in breadth is noticeable. 



Fig. 3. Outlines of specimens of the aurelia form (descendants of c), 

 from Lot 5, Table VIH. c to /, Successive stages of fission. Note the 

 greater breadth of the specimens not dividing (a and b). Same magnifica- 

 tion as Fig. 2. (235 diameters.) 



In row 14, Table YIIL, are given the constants for all the young 

 halves examined of the aurelia group ; that is, for the sum of rows 

 9 and 12. The coefficients of variation are, as might be expected, 

 increased by adding these two dissimilar groups. The fact that the 

 correlation between length and breadth is likewise increased, as com- 

 pared with what we find in either group taken alone, might not, 

 perhaps, be anticipated. These changes in variation and correlation 

 are environmental effects, to be studied later. 



(&) The Unseparated Halves after LengtJieiiing Has Begun. — 

 As we have already seen, the length of the halves increases as the 

 constriction deepens (see the correlation tables for length with depth 

 of constriction, Nos. XL (page 441), XLV., XLVI. ; compare also 

 the outlines of dividing specimens. Figs. 2 and 3). The coefficient 

 of correlation between depth of constriction and length is, for the 

 626 halves of Table XL, .6882; with each increase of 10 microns 

 in depth of constriction the length increases 4.30 microns. If we 

 include only the individuals in which lengthening has clearly begun 

 (thus omitting the uppermost row of Table XL), we find that for 



