IMK.HATFDX AM) DISPKHSAI, OF INSECTS : ODONATA. 281 



pvopci' relative phice ; and it is, as Swainincrdain says, purely a ques- 

 tion of apparatus and skill, as to how much developnieiit these 

 embryonal cells (ima<?inal discs) must undergo before we are able to 

 detect them. As development proceeds they assume more and more 

 of their imaginal condition. When no longer required the larval 

 organs or parts of them, are stripped off, by histolysis as well as by 

 ecdysis. 



In the e arlier days, when Weismann's researches were first given 

 us, many people supposed that histolysis took place first and develop- 

 ment afterwards, that the larva was I'cduced to a state similar to a 

 segmented ovum, and that thereout the imago was developed something 

 like the embryo in the egg. We now clearly understand that this idea 

 was much greater nonsense than Swammerdam's theory. Theemboite- 

 ment theory does indeed represent our present knowledge as accurately 

 as the resources and ideas available at the time could do so. 



The imago is there, from the first, so soon as the larva is fully 

 formed. Many of its parts are represented by only a few cells, and 

 are overlaid (emboxed) by many larval parts of only temporary use, to 

 be afterwards stripped oil' when they have served their purpose. 



Swammerdam knew nothing, as such, of imaginal discs or em- 

 bryonic cells, but he divined that, in the small larva, there existed the 

 imaginal wing, the imaginal antenniv, and the imaginal legs. He, of 

 course, knew they must be very small and were not occupying space 

 that he saw was occupied by larval structures. He foresaw, in fact, 

 all our present knowledge, wanting only that detail and elaborated 

 terminology that only actual observation can supply. 



He was, in this, as in some other matters, a genius and a poet, and 

 not the blundering idiot that he is implicitly represented to be by those 

 who deny and deride his theory. 



Migration and Dispersal of Insects: Odonata. 



By .1. W. TUTT, F.E.S. 



The great number of times that LUMiila iiiiaiiiiimnidata has been 

 observed on migration compared with any other species is very remark- 

 able, and Hagen says that this species is the one which he had himself 

 repeatedly observed. The migration already referred to as having 

 taken place in 1852^% was traced by Hagen from its origin to its ter- 

 mination. He states that in June, 1852, on a fine warm day, he 

 noticed about 9 a.m., over the Konigsthor, an immense swarm of 

 /,. iiiuvlriniantlata, flying into the town. At midday they were still 

 advancing in thick masses, and Hagen then went out of the town to 

 watch the Hight where there was a free space, and notes that for a 

 quarter of a mile towards Dewan, the flight was at about 80ft. above 

 the ground, whilst nearer Dewan it was lower, judged by the height of 

 the trees, whilst still nearer it was so low that, seated on a waggon, 

 Hagen was driven through it. Farther inforniation was afterwards 

 obtained, whicli tended to show tliat it originated near Dewan, whilst 

 the following day the flight was noticed at Karschan. The flight was 

 towards the east"! He considered it to be an instinctive migration, 



*This wii^ I.ihcUuhi iiirdlriiiKiriihild an<l tint J'lulrlnnn iliprc'^-oim as mentioned 

 (intf p. l.')4. 



