10 



SOME ASPECTS OF MORPHOLOGY 



defined appendages (antennae). To disregard the evidence of 

 metamerism afforded by this segment and to accept similar 

 evidence betrayed by the segments that follow renders his theory 

 untenable in so far as morphological values are at present 

 interpreted. 



A third view as to the segmental composition of the insect head 

 is based upon the conclusions of Hansen. In 1893 this well-known 

 Danish morphologist claimed the existence of a pair of reduced 

 but true appendages situated between the mandibles and the first 

 maxillae in most Apterygota and some of the more primitive 

 pterygote insects. He termed these appendages maxillulae, since 

 it appeared probable that they are homologous with the first 

 maxillas (maxillulae) of the Crustacea. In his most recent studies 

 Hansen (1930) confirms his earlier opinions and brings forward 

 more detailed evidence in their support. If this contention be 

 well founded it follows that the insect head would have to be 

 interpreted as being composed of seven segments, as shown below. 



Comparison of the above table with that given on p. 5 will make 

 it evident that these seven suggested segments do not entirely 

 correspond with those recognised by Wiesmann. In the Collembola, 

 for example, Hansen claims that the maxillulae have hitherto been 

 identified as maxillary palpi notwithstanding the fact they are a 

 perfectly free pair of mouth-parts with separate articulations. 

 In Japyx the maxillulae likewise have separate articulations and 



