MIGRATION AND DISPERSAL ON INSECTS I DIPTERA. 173 



course was unknown) nearly 25 per cent., (2) ab. ftava, working out at 

 about l-i per cent., the remainder being (3) ab. quadrata and (4) the 

 usual second-brood form of the species in about equal proportions. 

 The size of the specimens in almost every case was equal to those 

 of the June brood, and, in some instances, the males were even 

 larger, doubtless owing to an abundant supply of food. On September 

 12th a ^ example of a,h. jlava having slightly rubbed its thorax in the 

 cage, I decided to pair it if possible with one of its own form, should 

 one emerge in time, but the next day a $ of the ochreous aberration 

 appeared, and, fearing to miss a chance, although I should have 

 preferred pairing it with an example of nh. flaca, I kept this alive also 

 in the same box. I noticed ova on the 16th and succeeding days, 

 most of which hatched out on September 26th. Placing the young 

 larvae on dock and maintaining them at an ordinary room temperature, 

 I was surprised after they had been feeding about a fortnight to find 

 that a dozen were feeding more rapidly than the rest, and appeared 

 likely, although then late in the year, to feed up. With this view I 

 separated them from the rest, and, placing them in a warm position, 

 with a liberal supply of fresh dock, they duly pupated during 

 November. Of this third brood nine specimens ultimately came out, 

 the first on December 8th, and the last on the 21th of that month (three 

 dried up in pupa), Avith the result that all the nine followed in 

 colour and markings either the male or female parent, not a single red 

 specimen appeared. Three were of the male form, whilst six were 

 of the darker yellow tint and had the markings of the female parent. 

 By the success that attended the breeding of these two forms I 

 appeared to get convincing proof of the existence of two very interest- 

 ing and well-defined yellow aberrations of Noctna rubi. The remainder 

 of the third brood larvji? have been successfully hybernated and are 

 now in the pupal stage. 



Migration and Dispersal of Insects: Diptera. 



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

 The actual records of the migration of diptera are very few indeed, 

 and those that bear somewhat on the subject appear to refer rather to 

 dispersal movements on a small scale than to definite migration. 

 Wallace, however, notes [Geoij. Dist. Aiiimah, p. 82) a casein which a 

 southerly wind brought flies in myriads to Admiral Smyth's ship in 

 the Mediteranean when he was 100 miles distant from the coast of 

 Africa ? Scudder, too, made an observation on the movements of 

 certain diptera, at Little Boar's Head, N.H. He states [Psrjchc, v., pp. 

 402-103) that, on the afternoon of July 27th, 1890, he was sitting on the 

 shore there backed by a bank, when his attention was directed to the 

 constant southward movement of small flies. There was practically 

 no wind, but the flies moved swiftly in one direction for the space of 

 two hours, forming a stream such as might readily pass through an 

 open barrel. Their numbers varied, at times three or four would pass 

 a given point every second, at other times hundreds, but, on the average, 

 there were about as many in the given area as drops of rain in a smart 

 shower, rarely one would be seen moving out of the stream, and then 

 it was in a diametrically opposite direction, and just as swiftly. He 

 adds that the direction was evidently influenced in part by the trend 



