1913 ENTOMOLOGICAL SOCIETY. 93 



As we glance over the Hexapods we find comparatively few adapted to aquatic 

 life, not one single order which is wholly aquatic tHiroughout the larval and 

 imago states. The Ephemerida, Odonata, Plecoptera, Trichoptera are all aquatic 

 in the larval state, the adults being aerial. Part of the Neuroptera, some rare 

 Lepidopterous forms (Hydrocampa, Paraponyx), are aquatic in the larval state, 

 and several large families of Hemiptera and Coleoptera are aquatic throughout 

 their entire existence. Yet the species comprising these families are nearly all 

 terrestrial in their mode of obtaining their air supply. Some rare hymenopterous 

 forms are also aquatic, parasites on the eggs of various insects which depost their 

 eggs in water. As yet but few of these parasites have been reared, though un- 

 doubtedly many exist. It is an inviting field for anyone interested in discovering 

 new things. 



Despite the comparatively few species of insects, probably not more than 

 15,000, which are aquatic in their habits, we find here some of the most remarkable 

 adaptations. In the May-fly group alone we find the various genera adapted to 

 the most diverse aquatic environments. We find them in the swiftest streams 

 and waterfalls (Heptagenia, Epeorus, Iron, etc.), in more or less stagnant ponds 

 (Blasturus, Siphlurus), in the quieter streams and riffles ( Callibaetis, 

 Leptophlebia), and burrowing in the mud and ooze at sides or bottoms of ponds 

 (He:»Egenia, Caenis, Tricorythus, Ephemerella). Some of the May-fly species are 

 admirably adapted to one particular environment as those of Iron while others are 

 capable of living under a greater diversity of conditions (Leptophlebia, 

 Ephemerella). In nearly all the aquatic groups we find more or less of a parallel 

 development, each species well adapted to the situation in which it lives. 



I shall not attempt a detailed discussion of the various modifications which 

 were necessitated by the change from a terrestrial to an aquatic environment. 

 Probably the most difficult situation which the aquatic forms had to meet was the 

 securing of air supply. And to solve this difficulty we find insects have developed 

 a great variety of structures. And these structures have certainly developed 

 independently in widely divergent groups. There are practically two methods by 

 which any form can secure its air supply. (1) By coming to the surface and 

 breathing air directly, (2) By means of either tracheal gills or blood gills and 

 thus making use of the air dissolved in the water. 



I shall discuss the first method hurriedly. Those forms that secure their air 

 supply directly at the surface are found in widely separated orders. Many of 

 these species have developed very complicated and beautifully adapted structures. 

 In the Hemiptera many forms have developed pile on the surface of the body 

 enabling them to carry down an air supply (ISTotonectidae). Very little is known 

 concerning the methods by which members of the family Belostomidae secure their 

 air supply. In Belostoma there are areas of pile on the under surface of the body 

 by means of which an air supply is carried. The antennae are wonderfully 

 modified, somewhat analogous to "that found in the Hydrophilidae but it is not 

 known whether they are used in securing an air supply. In Nepidae the caudal 

 stylets have been modified into a tube which is pushed through the surface film 

 and thus an air supply is obtained. The aquatic members of the Coleoptera also 

 take down an air supply. In the Haliplidae I found quite a new adaptation for 

 securing air (Jour. N.Y. Ent. Soc. xx, pp. 180-181, 1912). Everyone is familiar 

 with the method by which members of the Dytiscidae secure their air supply. In 

 the Hydrophilidae the terminal club of the antennae which is pilose acts as the 



