On Aquatic Carnivorous Colcopte7-a or Dytiscidce. 245 



pigment, and has besides lai-ge sharply defined patches of nearly black pigment. 

 In Pelobius the basal portion of the wing is pigmented with yellow, while the 

 outer portion is smoky. 



The wings of the Dytiscidse in their neuration vary very little and are extremely 

 similar to those of the Carabidse and Cicindelidee so that no certain character can 

 be pointed out as distinctive. Usually the anal area is larger in the Dytiscidfe than 

 it is in the Carabidse, but in the Noterides this part is quite as small as in the Cara- 

 bidaa. The oblong pigment mark near the middle of the hind margin appears to be 

 wanting in the Carabidre, but is also frequently absent in the water beetles 

 (Bidessus, Eretes). In Amphizoa the pigment mark is very largely developed, but 

 the anal area is rather small ; in Pelobius the pigment mark is absent, and the 

 anal area is small as in the Carabidse. 



I have already mentioned that in one species of the family (Colymbetes bifarius 

 No. 757 Agabus) the wings are rudimentary : on careful examination of this species, 

 the costal, subcostal, and median veins are found to exist, as does also the accessory 

 vein between the subcostal and median veins, and even the flexuous adjunct to the 

 latter ; and the pigment mark is largely developed ; the interior portion of the 

 wing is however scarcely represented, a portion of the submedian vein is indeed 

 present and forms the boundary of the wing, but the parts that should lie internal 

 to this are quite undeveloped. 



Although the Dytiscidoe live in watei", they are only adapted for aquatic life by 

 modifications almost confined to their external structure. As however, owing to the 

 modifications of their legs for swimming, they are very ill adapted for walking, it is 

 highly important to them that they should possess wings to transport them to fresh 

 localities when, as very frequently happens, the pools of water in which they have 

 been living dry up. That these dwellers in the water should possess highly developed 

 wings is not therefore so peculiar as it at first sight ajjpears ; but it certainly is 

 a remarkable fact that their wings should be so extremely similar to those of the 

 Carabidas and Cicindelidfe. The Cicindelidee especiall}^ are verj^ rapid runners, and 

 take very frequent short flights, opening their wings with extreme haste, to enable 

 them to pounce on their prey ; the Dytiscidse on the other hand, only very rarely 

 fly, their flights are then probably for long distances, and the insect only takes to 

 flight at all with difficulty and after a laborious preparation of itself for the jiurpose ; 

 it is then certainly a most remarkable fact that the wings in these two families 

 should be so extremely similar. 



The development of an elegant pigmentation on the wings of certain species of 

 the family (especially Hydaticus flavolineatus No. 1024) is specially worthy of the 

 attention of those who may be engaged in considering the origination of colour in 

 insects ; the wings in the Dytiscidse ai'e completely withdrawn from all the external 

 influences that may be supposed to regulate the development of colour and pattern, 

 and yet they show extreme differences in the development of pigment, and when 



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