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appreciated, the arrangement reminded me very much of individuals 

 one occasionally meets with, who encircle their plate with the left arm. 

 The object of the manoeuvre is probably similar in the two cases. In 

 that before us, to prevent the escape of exuding sap from the bitten 

 parts on to those just cleared, and also its rapid loss by evaporation. 



These processes are long, broad at the base, and narrowing to a 

 blunt point. They seem to have two lines across them, making them 

 like true legs with three joints, and they have a dark corneous tip. 

 They have, however, no other corneous plates or appendages, the 

 corneous point has a few very minute terminal hairs. 



On first trying to see what these processes really were, the con- 

 clusion was almost irresistible that the prothoracic leg was double, 

 as this process arises in front of and to the inner side of the true 

 leg, and at first glance from the same base, and the true leg is very 

 short and stumpy, and apparently with only one or two joints ; as 

 regards segmentation, &c., this process seemed the better leg of the 

 two. This, however, being scouted as an absurdity, the next point 

 was, whether it was a form of chin gland. This idea was suggested 

 by the fact that the process is retractile, or rather erectile, when the 

 larva is not eating, it is not visible, and is quite flattened down. Its 

 situation, however, is too far from the middle line for this, the two 

 processes (of either side) being very far apart at their bases. 



Lines of muscular tissue may be seen traversing the length of 

 the process for its retraction. Similar strands run into projections of 

 the 2nd and 3rd thoracic segments, which project in similar positions 

 in relation to the legs of these segments to that held by this process 

 on the Ist ; the projection on the 2nd is a large rounded boss when 

 erect, that on the 3rd is similar but smaller. 



On watching a larva feeding, one now sees that these processes 

 or bosses of the 2ud and 3rd thoracic segments are erected or swollen 

 out, and with the legs and that of the 1st thoracic, form, by pressure 

 against the leaf surface, a closed cavity surrounding the jaws and 

 other mouth parts, where at work on the leaf. Their use is doubtless 

 that I have suggested, to prevent the escape of sap from the bitten 

 surface, either by evaporation or soaking along the surface ; whether 

 they act also as the margins of a sucker promoting the flow of sap to 

 the part must be a matter of conjecture. They also form a support 

 by way of cushion and fulcrum, to maintain the head in proper 

 position relative to the leaf. 



Betula, Reigate : 



August, 1900. 



