I — The Metamorphosis of May-fly 

 Mouth Parts 



I— INTRODUCTION 



This paper is a study of the metamorphosis of May-fly mouth-parts. It 

 follows the development of mouth-parts in the embryo, and their changes in form 

 and structure in nymph, subimago and imago. 



The life cycle of a May-fly is divided into two main parts : a relatively 

 long period of development spent in the water; and a brief aerial existence de- 

 voted entirely to reproduction. The female either drops the eggs at the surface 

 of swift or stagnant water, or, as in Baetis, creeps into the water, and deposits 

 them on stones in tiny, single-layered patches. From the time of hatching, 

 nymphal activities are concentrated mainly on food and growth. Indeed, all the 

 eating for a life time takes place during this stage. When nymphal life is com- 

 pleted, the insect usually swims to the surface of the water, sheds its skin, and 

 flutters through the air to some support. There it sits, with wings uplifted, and 

 fore legs thrust stiffly forward, waiting for the subimaginal molt. Then the 

 imago or true adult emerges and joins an assemblage of its own species. A 

 mating dance follows. They rhythmically rise and fall in flight, soaring aloft 

 to various heights and falling ecstatically with wings outspread. Soon the 

 females leave the throng one by one, and fly away to deposit their eggs. The 

 males prolong the joyous revel until exhausted. A little later the dead bodies of 

 all are washed about in the water. 



II— TECHNIQUE 



Embryology. The principal material used for the study of the embryology 

 of the mouth-parts has been Baetis posticatus. The eggs were treated as follows: 



Hot water 1 minute 



Bouin's fluid 12 hours 



65% alcohol 72 hours 



75% alcohol 24 hours 



80% alcohol 24 hours 



85% alcohol 24 hours 



90% alcohol 24 hour. 



95% alcohol 24 hours 



Abs. alcohol 1 week 



The absolute alcohol hardened the embryos so that the outer membranes could 

 be removed without injury to the specimens. The eggs were stained 24 hours 

 with hydrochloric carmine, and differentiated with acid alcohol. Then they were 



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