266 



THE ZOOLOGIST. 



of the water, as these will not stand immersion, and once they 

 get wet the fly is quite helpless. After the deposition of the 

 eggs life seems to leave the insect, and it remains spread out flat, 

 * spread-eagle' fashion, in a condition that is technically known 

 to anglers as a * spent gnat.' I saw numbers of male insects 

 alight for a few seconds on the water, and then fly away. This 

 action on the part of the male gave rise no doubt to the supposi- 

 tion that ' after the eggs are passed into the water they are ferti- 

 lized by the male,'* for I noticed that the males frequently flew 

 on to the water just after oviposition. The oviduct is on the 

 eighth abdominal segment, and as soon as the eggs are laid two 

 small bladder-like sacs protrude from each side, filled apparently 

 with air, which readily burst when a slight pressure is used. 



" May 22nd. — Sweetwater. I arrived at the side of the water 

 at 6 p.m., and found the Mayflies in prodigious swarms, the 

 females predominating, and flying swiftly over the water deposit- 

 ing their eggs. The day had been very warm, and a soft south- 

 west breeze blowing. De Geer says, from his observations, that 

 ' the males greatly exceed the females.' " 



As it will be seen by the above notes, according to my own 

 observations, that on the first and second day only males were 

 seen ; therefore it is reasonable to assume that the males make 

 their appearance first, and live for a considerably longer period 

 than the females. According to the observations of former 

 years, I note that males always put in an appearance first. The 

 beautiful and wonderful dancing flight performed by the Mayfly 

 is chiefly enacted by the male insect, and generally when the 

 sun is very hot, and again towards tbe cool of the evening. If, 

 during their flight, the sun is hidden by a passing cloud, they 

 immediately sink to rest on a grass-stem. The female's one and 

 sole duty is, after pairing, to rest awhile and then deposit her 

 eggs ; after that she dies. The eggs when first laid are enclosed 

 in a thin transparent covering, which breaks as soon as it touches 

 the water, and the eggs are dispersed and sink at once. 



Eeference was made in a former paper (Zool. 1908, p. 459) 

 to the long anchoring threads attached to the eggs, and 

 these threads I detected myself under the high power of the 

 microscope. Wishing to get some eggs for microscopic examina- 

 * Swarnnierdamm, 11 Epheuieri vita &c." 



