Hale — Aquatic Hemiptera 407 



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friction ; the sound is often maintained for long periods ; in mid-winter one 

 example continued its song intermittently during the whole of one day, as is the 

 case during breeding. Stridulation commences with a rapid series of squeaky 

 notes, not loud, but continued for a minute or more ; the notes then become 

 slightly louder and more metallic, and finally merge into a shrill and loud chirrup, 

 which is not sustained, the song soon sinking to pianissimo or ceasing altogether. 

 When sitting near an aquarium containing stridulating Anisops, the effect is as 

 of a distant grindstone at work, with the sound borne very faintly to the ear. 

 Sometimes the characteristic chirrup is produced without the preliminary fainter 

 notes, and vice versa, but in any case the stridulation is quite easily distinguished 

 from the fewer and less quickly repeated notes of Corixids. 



Oviposition. It has been mentioned that an examination of the female, 

 genitalia of the Australian species shows that all insert their eggs in plants. 

 Some thick stems of Potamogeton tricarinatns, an indigenous water-plant, were 

 anchored close to the glass of an aquarium containing some of the bugs under 

 observation, and it was thus possible to watch the whole process of oviposition. 

 The female grasps a stem with the anterior and middle legs and curves the 

 abdomen so that its tip is almost touching the surface of the plant; the orifice 

 opens and the point of the ventral carina explores the stem, the insect meanwhile 

 walking down the support until a suitable site is selected. The genitalia are then 

 extruded, the point of the abdominal keel is firmly applied and kept rigid, and 

 quite close to it the drilling gonapophyses work at the stem with a circular, 

 scraping motion; the epidermis is soon penetrated and an oval cavity is gouged 

 out of the plant tissue. As the hole increases in size the tip of the carina slips 

 into it at the lower edge (the insect being head-downwards), while all the time 

 the drilling organs can be seen inside the semi-transparent stem, operating with 

 a characteristic gouging movement. 



When the hole is completed there is a short pause ; then an egg is inserted, 

 leaving a small portion of the anterior surface exposed at the mouth of the cavity. 

 Finally the sensitive lip of the pygidium moves over and about the exposed 

 portion of the egg, as if to make sure that all is well ; the silky hairs of the 

 posterior abdominal segments and ovipositor are doubtless to some extent 

 tactile. The actual drilling of the Potamogeton tissue occupied from 35 to 50 

 seconds, the insertion of the ovum about 15 seconds. After an egg is laid the 

 female swims- away, vigorously cleaning the tip of the abdomen with the posterior 

 legs and constantly exposing the genitalia while doing so. Oftentimes the female 

 settles on a stem, explores the surface with the closed tip of the abdomen, and 

 floats off again, as if dissatisfied with the location ; if the ovipositor is extruded, 

 however, one can be sure that, if not disturbed, the female will insert an egg 



