• WORKINGS OF HYLESINUS FRAXINI. 183 



on the cells of ibc vitreous. The cells of the retina have 

 their nuclei situated very far back ; these eyes have also a 

 sling-shaped muscle, which seems to have the function of 

 altering the distance between the retina and the lens. The 

 posterior eyes have no layer of rods between the retina and 

 the vitreous, but the cells of the retina are very large, and 

 have their nuclei at their anterior ends : they enclose very 

 large prism-shaped bodies in their interior at some distance 

 behind the nuclei, which Dr. Grenacher regards as percipient 

 rods. These eyes have no muscle. 



In the genus Lycosa the four small eyes on the forehead 

 belong to the first kind, whilst the four great dorsal eyes 

 belong to the second. 



In the genus Salticus the latter form of eye is extra- 

 ordinarily well developed ; six of the eight eyes belong to 

 this category, the anterior four occupying almost the whole 

 margin of the cephalothorax. 



In the simple eyes of perfect insects the retina is formed 

 on the same type as in the first form of eyes in the spiders, 

 but the vitreous is in general very little developed, so that 

 the rods of the retina almost touch the posterior surface of 

 the lens ; an exception to this is seen in the single stemraa 

 of the flea, where the cells of the vitreous are comparatively 

 well developed ; they are also more strongly developed in the 

 blow-fly than in most other insects, but they are not so well 

 developed in it as in the flea. 



(To be continued.) 



WORKINGS OF HYLESINUS FRAXINI. 

 By E. A. Ormerod. 



In the spring of 1875, the ash-boring beetles {Hylesinus 

 fraxini) appeared in such numbers on the trunks of some 

 newly-felled ash trees in the neighbourhood of Isleworth, as 

 to give an opportunity of watching their method of operation 

 and rate of progress, and a short note may be of interest 

 from their difference in some particulars to those of the well- 

 known Scolyti of the elm. 



The H. fraxini is mentioned by Stephens and Selby as 

 occurring in decayed ash trees, and by E. Newman (En torn. 



