THE LIFE-HISTORY OP THE WATER-BEETLE. 79 



5. The Life-History of the Water-Beetle PeloUus tarduf; 

 Herhst. By Fkank Balfour-Browne, M.A. (Oxon. et 

 Cantab.), F.R.S.E., F.Z.S., F.E.S., Lecturer in Zoolo^ry 

 (Entomology) in the University of Cambridge. 



[Received January 10, 1922 : Read Mavcli 7, 1922.] 



(Plates I.-III.) 



)StC7n7nc0'i/. 



The paper has been paragraphed under the following 

 headings : — 



\. The family Pelobiidfe, p. 79. 



2. Britannic distribution of F. tardus, p. 79. 



3. The Imago. 



(») Habitat and Habits, p. 82. 



{h) Longevity in artificial environment, p. 83. 



(c) Stridulation. p. 83. 



{d) Sexual differences, p. 84. 



4. The Life-history. 



{a) Oviposition. p. 84. 



{h) Incubation, p. 85. 



(c) Vital staining of Embryo, p. 85. 



{d) The Larva, p. 87. 



(e) Food of the Larva, p. 89. 



(f) Stomodreum of the Larva, p. 90. 



{g) Habits of the full-grown Larva, p. 92. 



5. The Life-cycle, p. 95. 



(1) The Family Pelobiidte. 



The family Pelobiidse contains the single genus Pelohius and 

 only four species, one of which is European, one Chinese, and 

 two Australian. The family holds a somewhat isolated position, 

 being related to the Carabidae and showing similarities of struc- 

 ture with Dytiscidse and other aquatic beetles of the series 

 Adephaga, these being due, according to Sharp (10)*, not to 

 close relationship but to adaptation to life in the water. 



(2) Britannic Distribution. 



The single European species is not uncommon in Britain, but 

 belongs to the Southern or "English" type, as defined by 

 Watson (16), being chiefly found in the Southern and Eastern 

 counties of England. It has been recorded from one Scottish, 



* The numbers refer to the bibliography at the end of the paper. 



