174 Dr. T. A. Chapman on 



I only gave them access to material on which to lay, 

 when I was at liberty to observe them, so that I was able 

 to follow the whole operation in the case of every egg that 

 was laid. 



I fed them occasionally on water, neither sugar nor sap 

 expressed from the sallow seemed to tempt them. They 

 took the water freely but with extreme slowness, as if it 

 had to be absorbed rather than swallowed. This was 

 accompanied by what might be called chewing movements 

 of the maxillae, labium and palpi. The centre of the 

 mouth parts could not be well seen during the sucking 

 process, but seemed to have a bag-like appearance. 



What made the examination of the whole process of 

 egg-laying so easy to observe, and therefore (comparatively) 

 so easy to understand, depended on the large size of the 

 insect, on its very placid nature so that when laying it 

 could be moved into any position and approached as closely 

 as necessary with a lens, without in any way disconcerting 

 it. It was further facilitated by the circumstance that 

 the most satisfactory way of looking at the process, viz. 

 in profile, was also the most obvious and easiest. The upper 

 cuticle of the leaves, beneath which the pouch for the egg 

 is made, is perfectly transparent and the rest of the leaf quite 

 translucent. 



The sallow on w^hich I found the Trichiosoma laying 

 belonged to the Cajprea group, but I do not know its name ; 

 it had a somewhat regular oval leaf, rather small, and in 

 the young state in which the eggs were laid it is quite 

 glabrous. This last seemed an important character to 

 the instinct of our sawfly. Having difficulty in getting 

 the desired sallow, I. tried the flies with other species of 

 Salix, but they refused all I tried except one that seemed 

 to me to have nothing in common with the original sallow, 

 except that its leaves were glabrous; this was a willow, 

 possibly Salix fragilis, grown in the vineyards at Locarno, 

 for training the vines on and for supplying withes for tying 

 them. In describing the leaves of these two species as 

 glabrous, I am not strictly accurate, they were glabrous 

 compared with other available species of Salix, and really 

 seemed so when only the immature leaves that suited the 

 Trichiosoma were uncritically observed, but they actually 

 had some hardly visible hairs that were more obvious 

 when the leaves matured. 



The leaves selected by the flies were those that were 



