202 HELEN E. M. PIXELL-GOODBTOH. 



if these determinations of age are to be made of general 

 use, it is important to eliminate as far as possible the personal 

 equation. This can be done to some extent by comparing 

 the number of giant nerve-cells in some constant region of 

 the brain. There appears to be a small decrease in the 

 number of these cells with age, as stated by Hodge (10), and 

 as has been shown also for the Purkinje cells of the human 

 cerebellum by Ellis (5) . However, the counting of them entails 

 much labour, and consequently the tables with these numbers 

 will be held over until next year, when I hope to have a 

 perfect series of brains at all ages. 



Further, the condition of the glands gives some clue, to 

 age, for in normal healthy bees their physiological condition 

 corresponds to actual age. 



The glands of the head that are being studied are the 

 pharyngeal, salivary, mandibular and maxillary as described 

 by Snodgrass (19) and Cheshire (2). In addition, a small 

 pair of glands has been discovered of which I can find no 

 previous mention (PI. 11, fig. 2). These occur one on each 

 side of the oesophagus as it emerges from between the supra- 

 and subcesophageal ganglia — that is, they are just in front 

 of the commissures. These oesophageal glands are almost 

 spherical, about 120 microns in diameter. From each proceeds 

 what appears to be the remains of a convoluted duct to meet 

 its fellow of the opposite side at an angle of 60° above the 

 ceosphagus and in close contact with the central portion of 

 the supra-oesophageal ganglion. 



For the full investigation of these various head glands much 

 study is still necessary, and experiments with intra-vitam 

 stains are being carried on. Some of the glands vary enor- 

 mously with the immediate function of the bee. The pharyngeal 

 glands, for example, become distended with secretion soon 

 after hatching and remain so during the two weeks that the 

 bee functions as a nurse. By the time that pollen gathering 

 is undertaken, these glands appear to be exhausted and in an 

 advanced hyperchromatic state which gives the collapsed 

 glands a necroiic appearance. The different histological 



