1120 The Zoologist— March, 1808. 



remove to fresh food. Morren believed that this occasion was the first 

 appearance of A. Persicae in Belgium, and that all its swarms migrated 

 from one spot. It feeds on a great variety of plants, peach leaves are 

 not its usual food, and it abounds in Europe generally. A long con- 

 tinuance of hot dry weather much developes the winged vivaparous 

 form of Aphides, and the : time of this result varies locally ; the 

 swarms that appeared successively here and there throughout Belgium 

 may not have been really migratory. Their numbers, which are said 

 to have darkened the light of day and to have hidden the walls of 

 houses, seem to prove that they did not all radiate from one focus. 

 Morren suggests that, as it first appeared very near the west coast, it 

 may have come from England, and cites Schizoneura lanigera as an 

 example of migration. The latter, of which one individual has been 

 calculated to multiply to a quintillion and to thirty times that number 

 of eggs in one year, is stated to have come from N. America to 

 England, and to have spread thence over Europe, but there is no proof 

 that it has migrated by long flights. Morren's opinion that in Aphides 

 generally the viviparous Aphis is winged appears to be incorrect. He 

 cites A. Persicae as an exception to this rule. The fact that a cold 

 atmosphere is the means of developing the perfect form of Aphides 

 was noticed in 1802 by Mr. Curtis. Passerini suggests that an artificial 

 atmosphere may be the means of continuing the preparatory state ad 

 infinitum, and of thus annulling the ultimate condition. At the end of 

 September, in 1866, the winged female of A. Persicae appeared in 

 abundance on the peach leaves at Wanstead. It is very different from 

 the common Aphis of the peach. 



4. R. Liguslri, Kaltenbach. — This species is widely different in form 

 from the type of Rhopalosiphum, and may be included in Liosomaphis, 

 with L. Berberidis, till it is established as a new genus. 



5. R. Nymphccce, Linn. — This and some others belong to a group 

 that is quite distinct from R. Lactucae and from R. Persicae, and is more 

 nearly allied to the limited genus Aphis. Passerini, in his ' Gli Afidi,' 

 makes R. Nymphaeae the type of his genus Siphocoryne, but in his 

 ' Aphididae Italicae,' he cites A. Xylostei as the type of that genus. 



Genus 4. Myzus, Passerini . 



Antennae remote from each other at the base, seated on a short 

 tubercle; first joint not dentate. Nectaries cylindrical, longer than 

 the tail. In other characters like the preceding genera. 



Typical species, Aphis Cerasi, Fabr. 



