1920] Richmond, Studies on the Biology of the Aquatic H ydrophilidce 79 



the rnaxillulse, which Carpenter noted in the Diversicornia, are to be 

 found at the sides of the hypopharynx in these forms and bear further 

 testimony to their primitive position. 



The following larval characters are considered primitive. 



1. True campodeiform type of body. 



2. Well chitinized integument. 



3. Head inclined. 



4. Ocular areas in groups of five. 



5. Antennae three-segmented and with their points of insertion nearer 



the externo-frontal angles than those of the mandibles. 



6. Labrum and clypeus distinct and well developed. 



7. Mandibles with a lacinia mobilis. 



8. Maxilla with a well -developed inner lobe. 



9. Presence of rudimentary rnaxillulse. 



10. Labium short with complex ligula and palpi. 



11. Gula well developed and attaining the occipital opening. 



12. Labium and maxillae inserted in a furrow on the under side of the 



head. 



13. Legs well developed; tarsi without claws but claw-like. 



14. Holopneustic type with annuliform spiracles. 



15. Cerci three-segmented. 



16. Ten abdominal segments. 



The number of eggs deposited and the manner in which they are 

 protected are both important in phylogeny. The eggs of the most 

 primitive genera are laid singly and without a silken covering or, at the 

 most, with only a slight covering. On the other hand, many eggc- are 

 deposited in a mass and enclosed in a complex case by the members of 

 those genera best adapted to aquatic life. 



The pupae of the most primitive genera have not been described. 

 The genera best adapted to water show a reduction in the number of 

 pronotal styli and an increase in the distinctness of the annulations of 

 these styli. The cerci become stouter and more complex, as shown by 

 the possession of spines, more distinct annulations, and bifid shape. 



The most striking character of phylogenetic importance which 

 appears among the adults is, without doubt, the number of abdominal 

 sternites. Those genera possessing six or more sternites have larvae 

 which show a small indication, at least, of their evolution from the primi- 

 tive type. Berosus and Laccobius still possess a vestige 1 of a furrow on 

 the under side of the head. All other Hydrophilidae have five abdominal 

 sternites 2 . Neither the antennae nor the tarsi are apparently stable 

 adult characters and the venation requires further study. 



: This evidently represents the former insertion of the labium and maxilla? in a groove on the under 

 side of the head, and is primitive for hydrophilid larva. 



1 Spercheus larvse show primitive tendencies but the adult possesses only five abdominal sternites. 



