Ephemera, the May -Fly. 153 



bottom of the water. The only difference between larva and 

 nympha is tliat the latter has sheaths for the wings, which are 

 rolled or crumpled up inside them. The banks of rivers may 

 often be seen to be completely riddled by these larvse, which 

 tunnel for themselves tubular galleries in the mud to the depth 

 of four or five inches. The larvje of some other members of 

 the Ephemeridse, instead of living under the sand, or in tubular 

 galleries, swim from place to place, as in the genus Gloe, while 

 others crawl on the ground and on aquatic plants. The abdo- 

 men of the larva and nympha of Ephemera vulgata is bordered 

 on either side by a row of gills which, by their constant motion, 

 serve to draw fresh currents of water to oxygenate the blood. 

 Each gill consists of two large tracheal trunks, in which smaller 

 air vessels ramify in all directions (Fig. N). In the imago state 

 the whole respiratory organization is changed, the tracheal 

 trunks or gills are cast aside, and the insect now breathes by 

 means of stigmata. 



The dissection of the insect is a matter of some difficulty, 

 owing to the extreme delicacy of the organs. The alimentary 

 canal consists of a short oesophagus, stomach with rudimentary 

 hepatic vessels, and intestine with its numerous renal or 

 urinary vessels. 



The stomach (ventriculus) is long and cylindrical, marked 

 by several constrictions. In the sub -imago state it is sur- 

 rounded by a distinct mass of secreting vessels of a very irre- 

 gular form, which contain numerous curious bodies, circular in 

 form, marked by concentric lines. These concentric lines seem 

 to show that the bodies are formed of fine threads coiled one 

 over the other, the thick end, in shape something like the head 

 of a snake, being free (Figs. I, J, K). 



In the imago state, these vessels have undergone a change 

 of form. Instead of the irregular mass spoken of above we 

 find now several membranous filaments attached to the outer 

 walls of the stomach and intestine, with the same enclosed 

 circular bodies. What can be the use of these bodies I cannot 

 guess, nor am I acquainted with anything at all similar to 

 them in any other insect. The side view of these bodies will 

 remind the reader of certain forms of Diatomacese, such as 

 NaviculcB and Fragillaria, etc. The lower portion of the intes- 

 tine is surrounded by a tangled mass of threads as fine as 

 a spider's web. These are numerous distinct vessels which 

 empty themselves a little above the anus. Fig. M repre- 

 sents two of these vessels magnified. 



The ovaries (Fig. Gr) consist of two almond-shaped organs, 

 which occupy nearly the whole of the abdominal cavity. The ova 

 are unattached, and readily separate themselves in water. It is 

 the possession of these ovaries that makes the insects such 



