EGGS OF BUTTERFLIES 115 



divided into four classes : (1) barrel-slmped, (2) 

 spherical, (3) tiarate or turban-shaped, and (4) 

 hemispherical ; or, if we consider their surface sculp- 

 ture, into three groups : (a) ribbed, (1j) reticulate, 

 and (c) smooth. These divisions run into each 

 other to a greater or less degree, and nearly all 

 possible combinations are found. With rare excep- 

 tions nearly allied forms closely resemble each 

 other, and the degree of resemblance is in general 

 an excellent test of afBuity. Not only can species 

 and genera be distinguished by oological charac- 

 ters, but many of the larger groups, even as far as 

 the broadest natural divisions of butterflies, may 

 not infrequently be defined in terms of the Qgg, so 

 that it even becomes a valuable aid to classifica- 

 tion. 



The barrel-shaped form is sometimes very much 

 attenuated at both ends, so as better to be de- 

 scribed as spindle-shaped, and it is nearly always 

 broader at the base than at the summit, so as to 

 merit the term pyramidal, sometimes much broader, 

 as in Speyeria. The truncate top is also very fre- 

 quently rounded and its edge inconspicuous, and it 

 then runs into the spherical or hemispherical class ; 

 but the true barrel-shaped group is always higher 

 than broad. The Nymphalidae and Pierinae al- 



