CLASSIFICATION 323 



middle of the yellow face, while in V. germanica the band is 

 narrow, sometimes reduced to a spot, and there is a black 

 spot on either side below. In both these species and also 

 in V. aiistriaca the yellow and black markings of the abdomen 

 are sharply defined, but in V. rufa the edges of the black 

 markings pass into reddish-brown. The face of V. rufa is 

 like that of V. vulgaris, the face of V. austriaca like that of 

 V. germanica. These differences of form and pattern 

 between the various kinds of British wasps are of the type 

 used in discrimination of species, and within the same 

 species the characters are fairly constant. There are, 

 however, very definite structural specific characters which 

 become apparent from study of the male genital armature, 

 and these on account of their obvious biological and genetic 

 importance are often of greater value in specific distinction 

 than conspicuous features of colour and pattern. As 

 already mentioned in Chapter IX (pp. 234-5), ^- ^^f^ ^^^ 

 V. austriaca are, in the form of the male armature, more 

 closely related to each other than either is to any other British 

 wasp. The males and queens of V. austriaca, which appears 

 to have no worker caste, are reared in nests of V. rufa, 

 as if the former were a " guest " of the latter, but there is 

 considerable evidence for the view that the two are alterna- 

 tive varietal forms of one species. The British wasps afford, 

 therefore, an illustration of the difficulty often found in 

 deciding whether two distinguishable insects should be 

 regarded as distinct species or as varieties of one species. 

 Where it can be proved that two or more forms may arise 

 from eggs laid by the same parent, or can be traced back 

 through an observed and recorded series of generations 

 to a common ancestry, specific identity becomes certain. 

 But the classifier of insects is often in doubt as to the limits 

 of the groups that he seeks to define as " species," *' sub- 

 species," '' variety," and '* aberration," as well as of the 

 more comprehensive groups known as the genus, the family, 

 and the order. This frequent uncertainty as to definition 

 is one of the fascinating puzzles that confront the student 

 of biology ; while it gives ground to the critic for the charge 



