the Egg-laying of Trichiosoma. 177 



insect was free, so that taking the insect in profile, the 

 whole process was very easily seen, the saw within the 

 leaf being but little obscured by the translucent leaf 

 substance below it cutting off the light. Nothing, however, 

 could be seen from the lower side of the leaf owing to the 

 thickness of the leaf substance between, which, though 

 translucent, was by no means transparent." 



" When the saw is first seen to have really entered the 

 leaf, the darker posterior (in the then position of things) 

 portions of the saw (the ' supports ') advance slowly, 

 steadily and uniformly together ; whilst the anterior mem- 

 bers (the ' saws ') are seen to be in rapid motion." 



To understand the method of this movement, it is neces- 

 sary to remember the structure of the whole terebra. 

 This, as it exists in Trichiosoma, is shown in the photograph 

 on Plate XV, and in figs. 11 and 12 of Plate XVI. 



Mr. Morice calls attention to the fact that these terebrae 

 present in different species, different relative developments 

 of the " saws " and " supports," no doubt in accordance 

 with slightly different methods of operation according 

 to the requirements of each species in regard to the material 

 in which the eggs are laid and their disposition therein. 

 The justification for my recording my observations is 

 that in Trichiosoma the details of structure and procedure 

 do differ from those observed by Mr. Morice in Phymatocera 

 aterrima, Kl. In that species both saws and supports 

 terminate together in what forms an acute point to the 

 terebra, which apparently makes its first entry by a process 

 of stabbing. In Trichiosoma there are no sharp points, 

 the saws continue round the ends of the support, so that 

 the end of the terebra is not a point, but a continuation 

 of the cutting edge of the " saws," which even go round 

 the support so far that the cutting edge at their tips faces 

 in a posterior rather than an anterior direction. 



Mr. Morice tells us that these terebrae are not merely 

 objects in two dimensions but in three, and have a thick- 

 ness that in some species probably enables them to act 

 more or less as wedges. Though an object of two dimen- 

 sions only is a mere mathematical abstraction, nevertheless 

 in Trichiosoma the whole cutting action takes place in 

 such a way that we need not take into account that it 

 has any thickness, it is indeed so thin that one almost 

 wonders how it can possess the necessary strength. Each 

 saw and support has indeed a structure much like that of a 



TRANS. ENT. SOC. LOND. 1914. — PART I. (JUNE) N 



