36 THE FLEA [CH. 



all with beetles and Gross can find no signs of 

 relationship with either Coleoptera or Diptera. 



Embryology and the study of larval forms have 

 thrown so much light on the ancestry of many 

 animals, that it was hoped that a microscopic 

 examination of the larvae of fleas, in various stages 

 of development, would produce some facts of im- 

 portance. In this hope entomologists have, to a 

 great extent, been disappointed. There seems to 

 be much similarity between the embryos of beetles, 

 moths, flies, wasps and fleas. Those who have dwelt 

 on the likeness of the larval flea to the maggot of a 

 fly seem to forget that the resemblance to an embryo 

 beetle is nearly as strong. 



The young larva of the flea is very transparent 

 and the digestive canal, heart and nervous system 

 are easily recognised. The egg-shell breaker is an 

 interesting example of the development of a tem- 

 porary larval structure and it is the only known 

 instance of such a structure in an insect. There 

 are no traces of eyes. The antennae are three- 

 jointed. They are rather long and slender, being 

 about one-third as long as the head. The head is 

 well-developed and the larva has no feet. 



The biting mandibles are broad and triangular. 

 Compared with those of other larvae they are said 

 to be more like the mandibles of coleopterous than 

 of dipterous larvae. The maxillae, or second pair of 



