298 NATURAL HISTORY OF AQUATIC INSECTS CH. 



of air will be seen to issue. In a dried larva torn 

 across, the air-tubes are very easily seen, for they 

 retain their shape, and remain open when all the 

 other parts have dried up. The six large gills which 

 stand out from each side of the body are all provided 

 with large air-tubes, three to each gill, as also are the 

 five pairs of golden-yellow fins beneath, by means of 

 which the larvae swim.^ Some other observations 

 which I had made upon the gills and their vessels. 

 have been lost, and I cannot recollect what they 

 were. I do not know, for instance, what is the use 

 of the plume attached to the first pair of gills, and 

 I can now give no more information about them than 

 can be gathered from the figure.- 



" The heart lies on the dorsal surface as in other 

 Insects. It swells out in the middle of each segment, 

 Just as Malpighi represents it in the Silkworm. I do 

 not agree with this author in saying that the larva is 

 furnished with more than one heart, and I have only 

 very rarely seen any contraction of the heart in the 

 larva of Palingenia. 



" The nerve-cord consists of eleven ganglia. From 

 the first of these, or brain, the optic nerve can be seen 



^ In Palingenia, as in many other Ephemerida;, each tracheal 

 gill consists of a plate or lamina and a bunch of respiratory 

 filaments. Swammerdam calls the lamina; " gills," and the 

 filaments " fins," though both form parts of one set of organs. 



- In addition to the six gills described by Swammerdam 

 there is another in front, probably the plume referred to in 

 the text. The lamina of the fore pair in Swammerdam's figure 

 is too large in comparison with those which succeed (Vayssiere) 

 Org. d£s Larves des Epheincrines, Ann. Set. Nat. Zoo/. 18S2, 

 p. 5). 



