102 THE UNIVERSITY SCIENCE BULLETIN. 



the aquarium was seen to crawl up the side of the jar bearing an adult 

 female Mesovelia with its beak attached near the caudal end of the 

 fly, which when disturbed flew to a nearby support, bearing the tenacious 

 little bug. 



However, the writer has come to believe that, with Hydrometra, 

 Microvelia and Rheumatobates, they are not dependent upon the chance 

 and uncertain fare of terrestrial insects caught upon the surface film, 

 but find another, and indeed a more constant source, in the organisms 

 that dwell below but come up to the surface film. Among these, 

 Ostracods and like forms are available as more or less staple food and 

 Mesovelia have been observed exploring the sides of floating Typha and 

 the tangled mats of algae for such Crustacea which they spear from the 

 surface of the water. 



The tiny nymphs feed upon more gentle organisms in the water, 

 as there are few upon the surface that they are able to overcome. When 

 offered springtails, as suggested by Butler, disaster often followed, and 

 the writer lost many good rearings before he learned the inadvisability 

 ■a£ offering such food. The hungry little creatures would attack them, 

 only to be turned topsy-turvy upon the water, even by comparatively 

 small springtails. Plant lice afforded less risk of this kind and gave 

 better results. They were used as the food supply in the isolation rear- 

 ings where a study of molts was made. But in an aquarium 12 inches 

 in diameter, the water of which contained algse and floating sedge stems 

 amongst which dwelt an abundant population of Entomostracans, the 

 little bugs were reared through their complete cycle without other re- 

 source than that afforded by the waters and the weaker of their own 

 kind. 



Mating. In mating the male mounts the female, clasps his fore legs 

 around her mesothorax in front of her middle legs, rests his middle legs 

 upon the water film or other supporting surface, and holds the hind legs 

 poised in the air. The copulatory organ of the male is long and curves 

 around the side of the tip of the female's body to come into contact 

 with the genital opening. Contact lasts from a few seconds to one 

 minute or longer. Upon withdrawal the copulatory organ is seen to be 

 a slender white tube of astonishing length. 



Oviposition. Since Mesovelia hides and protects its eggs by burying 

 them in the tissues of certain plants that are associated with shores 

 and shallow waters, the female possesses an ovipositor adapted to this 

 purpose. If the female be examined in lateral view, the abdomen is 

 seen to be laterally compressed at its caudal end in such a manner as 

 to provide a sheath or groove for the ovipositor. A dissecting needle 

 inserted near the distal and caudal end of this fissure can be used to 

 pry out and bring to view a shiny brown chitinized organ which may be 

 turned down into a position approximately at right angles to the body, 

 for its attachment is at the basal end of the sheath. In this position 

 it is seen to be curved so that the tip is directed slightly forward. The 

 general shape, viewed from the front, is roughly spear-shaped and the 

 parts arranged in such a way that the front surface is concave, form- 



