Sept. is, 1916 Dwarf Eggs 999 



(b) the relative tonus of the two sets of muscle fibers of the oviduct wall. 

 A decrease in the tonus of the circular fibers, or an increase in that of the 

 longitudinal fibers, or both, may counterbalance the increase in pressure 

 due to increase in the diameter of the egg. There is no a priori reason 

 for assuming a correlation between breadth and length; in fact, this 

 correlation was not significant in the random sample of normal eggs 

 studied by Pearl and Surface (20). From this they concluded that the 

 two sets of muscles are to a large extent independent in their action. 

 On the other hand, Curtis (4) found that within the normal eggs of an 

 individual there is usually x a significant correlation between length and 

 breadth — that is, the size of the active oviduct and relative tonus of 

 the two sets of muscle fibers in the oviduct wall are apparently usually 

 relatively stable in an individual, and an increase in the breadth of the 

 egg is correlated with an increase in the length. The fact that the 

 correlation between length and breadth is significantly higher (Table 

 XXI) for dwarf eggs than for normal eggs may indicate that in these 

 small eggs there is little or no differential stimulus on the muscle fibers 

 of the oviduct wall, but that there is such a stimulus when the egg is 

 larger. 



2. Length and breadth are both highly correlated with weight — 

 that is, a heavy egg is both broad and long. These relations are also 

 true for normal eggs. The random sample of eggs studied by Pearl and 

 Surface (20) showed a correlation between breadth and weight which was 

 significantly higher than the correlation between length and weight. 

 The individual birds studied by Curtis (4) showed a great variation in 

 the relative degree of correlation of the two dimensions with the weight. 

 Half the flock showed a correlation for breadth and weight significantly 

 higher than for length and weight. Tw r o birds showed a higher length- 

 weight correlation. For one-third of the flock the difference was in- 

 significant. There is no significant difference between breadth-weight 

 and length-weight correlation in any class of dwarf eggs. (See Table 

 XXI.) 



3. The index-weight correlations are negative, and they are significant 

 for dwarf eggs with little or no yolk — that is, for those two groups of 

 small dwarf eggs the larger the egg the longer it is in proportion to its 

 breadth. In the study of the normal eggs of individual birds Curtis 

 (4) found that there was a low negative correlation between index and 

 weight which was significant for one-half of the individuals studied. 

 This tendency toward a negative correlation between index and weight 

 in dwarf and normal eggs is in line with the fact that the mean index 

 of the several groups of dwarf eggs, normal eggs, and multiple-yolked 

 eggs varies in the opposite direction from the mean egg weight of each 

 group — that is, the larger the egg the lower the index. The bearing 

 of this fact has already been discussed. 



1 In 18 out of 22 individuals studied. 



