128 THE entomologist's record. 



of the proboscis are firmly held together, and no friction here causes 

 the sound. In the interior of the head, facing the lumen of the pro- 

 boscis, is an opening, capable of varying its form from nearly circular 

 to a narrow slit ; this opens behind into a cavity of a diameter of 

 about 2mm. lying immediately behind the clypeal region. This 

 cavity has walls of fairly fixed position below and laterally, being con- 

 ditioned by the surrounding chitinous structures of the head ; but 

 above it is not in contact with the walls of the frons and vertex. The 

 space here between the frons and this special sac cavity is occupied by 

 a rete mirabilc of tracheal tubes, and over this area the roof of the sac 

 is soft and flaccid, and capable of considerable movement, so much as 

 to amount probably to complete collapse of the cavity when it is 

 depressed. This cavity appeared to be a dilated upper end of the 

 oesophagus, its structure appearing to be continuous with the oesopha- 

 gus, but I did not succeed in passing a bristle from the cavity into the 

 oesophagus. The primary function of this cavity seemed probably to 

 be to produce a sucking vacuum at the base of the proboscis to draw 

 up honey or other fluids, its method of action being the alternate 

 turgescence and exhaustion of the tracheal spaces above and also 

 around it, produced probably by the abdominal movements, and 

 utilised by the valvular action of its openings. It seemed to me that 

 air either drawn into or expelled from this sac, through the valvular 

 opening at the base of the proboscis, was the cause of the cry. I 

 entirely failed, however, to obtain a vieAv of this opening or chink 

 during vocalisation, and so am unable to feel absolutely sure that this 

 is really a vocal organ. That my conclusion, however, is the same as 

 Mr. Moseley's, and was reached without the prompting of previous 

 information, gives his view strong support. — T. A. Chapman, M.D., 

 F.Z.S., F.E.S., Betula, Reigate. 'Februanj 12th, 1901. 



J^RACTICAL HINTS. 



Field Work for April and May. 



By J. W. TUTT, F.E.S. 



1. — The eggs of Gonepteryx rhamni may be found in April and 

 May on the leaves and petioles of llhannuts franijiila. 



2. — In May, 1901, examine the ends of the birch stumps cut down 

 in the winter of 1899-1900. The frass of the larva of Sesia culici- 

 fonnin between the bark and wood will tell where to look for the 

 caterpillar itself. 



3. — Xnla cristidalis sits head downwards on the stems of privet, 

 beech, hornbeam, birch and oak in early May; rather conspicuous on 

 beech and hornbeam. 



4. — Beating in May for " hooktips " is often profitable. Drcpana 

 cultraria, lacertinaria, falcataria and hinaria are abundant in most 

 southern woods with the right growth. The males of D. cultraria fly 

 about freely in the sunshine, and sometimes those of 7>. hinaria are to 

 be seen flitting in the glades of the woods of our south-eastern counties. 

 The Fairmead district of Epping Forest is a good locality for l>. 

 binaria. 



5.- — The larva of Geometra papilionaria is to be found in April and 

 May sticking out from the tips of birch twigs, and closely resembling 

 the birch catkins. 



