258 THE ENTOMOLOGIST. 



throw some light on the length of time that JE. cyanea spends as 

 a nymph, and also on the number of times it changes its skin. 

 In January of this year two or three nymphs were taken from a 

 pond in my garden, and these measured 20 mm. each. Together 

 with others from the same pond, they have all (with one excep- 

 tion) changed into perfect insects. In July of this same year 

 nineteen small nymphs, 10-17 mm. long, were found in the pond, 

 this date being of course long anterior to the time when M. cyanea 

 begins ovipositing. It may of course be thought that these are 

 only some belated specimens, but it will, I think, be agreed that 

 this supposition cannot be maintained when it is stated that 

 during August more than two hundred nymphs, all of about 

 this size, were taken from the same pond. In confirmation of 

 the view that these are last year's laying, I was fortunate 

 enough to find in one aquarium, on July 30th of this year, a 

 solitary nymph 10 mm. long, and upon searching the aquarium 

 three empty skins were found, measuring respectively 6|- mm., 

 5 mm., and 3^ mm. Now, looking to the fact that the egg of 

 Anax imperator (according to Mr. Lucas) is 1§ mm. long, this 

 smallest nymph skin, measuring 3^ mm., must be the first or 

 second skin cast. The nymph is now 20 mm. long, and has cast 

 since first observed seven skins, so that at 20 mm. long we may 

 say that the nymph has cast eight skins at least, possibly nine 

 or ten. The observation will, if possible, be completed next 

 year ; but I venture to give this information now, as, owing to a 

 fortunate accident, these earlier changes, which are the only dif- 

 ficult ones to observe, have been recorded. 



The two hundred nymphs referred to above, or rather those 

 that remain uneaten by the survivors, now measure about 

 17-22 mm., will, I imagine, grow but little during the winter, 

 and will be ready to come out next June or July, thus giving 

 two seasons as the normal time for the growth of the nymph 

 of M. cyanea. I have, however, one nymph almost full grown, 

 which has been very slow in growing all this year, and which 

 may, not improbably, be unready to change before the season is 

 too far advanced ; if so, it will no doubt come out very early next 

 year, giving the impression that it belongs to a different hatching 

 from those which came out last July, which it does not. 



A very interesting point remains as to when the nymph 

 3^ mm. long mentioned above was hatched. Unfortunately, I 

 cannot say precisely when it got into my aquarium ; it was cer- 

 tainly not before January of this year, and it may have been as 

 late as June ; in any case, the earliest stages of all must be ex- 

 tremely slow, or the eggs must remain unhatched for several 

 months ; possibly the eggs lie dormant from November or earlier, 

 during the whole of the winter, and are hatched in spring. 



Observations have been made on forty- six adult nymphs (all 

 of Mschna cyanea) this year. All climbed out of the water to 



