1922] Uichanco — Notes on Parthenogenetic Macrosiphum 71 



that they do not follow any regular schematic sequence. Further, 

 it appears that no two legs move synchronously in the same 

 direction, and that there is no definite rule as to the order in 

 which the legs follow one another. The time intervals between 

 successive steps, irrespective of the sequence of leg movements, 

 appears to be maintained at a uniformly similar rate for a given 

 speed. 



Summary of Section II. 1. The principal method of 

 locomotion, even in alate individuals, is walking, the feeble 

 wings being used rarely. 



2. The rate of diagonal swaying of the antennae and the 

 rapidity of walking appear to be correlated, the movement of the 

 former being in direct proportion to that of the latter. 



3. The movement of the legs do not follow any regular 

 schematic sequence, although the time intervals between suc- 

 cessive steps appear to be uniformly maintained in a given speed. 

 No two legs move synchronously. 



III. Feeding Habits. Macrosiyhum tanaceti has been 

 known to occur only on Tanacetum vulgare Linnaeus. This 

 species of aphid apparently has no secondary host plant. 



No attempt will be made in the present work to describe 

 the mechanical and physiological relation of the mouth-parts to 

 the plant tissue during the process of feeding. Considerable 

 work has been done in connection with this problem in com- 

 paratively recent years, notably by Biisgen (1891), and by 

 Zweigelt; the latter author has been working on this and related 

 subjects during the past decade. Zweigelt (1915) suggests the 

 following three possible means by which suction of plant sap is 

 accomplished in aphids. 



"1. Eine bestimmte Zelle wird angestochen und ohne 

 Verletzung der ausseren Hautschicht des Protoplasten ausge- 

 saugt; 2. die Aussaugung bestimmter Zellen erfolgt wahrend 

 deren vollstandiger Durchbohrung; 3. die Aussaugung gcht 

 zufolge einer dem Speichel innewohnenden starken osmotischen 

 Saugkraft bei interzellularem Stichverlauf ohne mechanische 

 Verletzung der Zellen vor sich." 



