intercaste adults. They only become determinate queens late in the В period 

 after the legs and ovary have divided. 



Larvae at various stages were sectioned and stained with Gomori's paral- 

 dehyde-fuchsin and Groat's iron haemotoxyHn, following a method developed 



Fig. 1. a — d brain neuro-secretory cells; e — g cells of corpora allata. a from A period 

 spring larva showing j^urple granules black; b from В period queen larva with grey cyto- 

 plasni; с from В period worker larva with only a few purple granules; d from A period 

 autumn larva; e from В period worker larva; f from В period queen larva; g from large A 



period larva in November. 



by Gabe (1953) and by Fraser (pers. com.) This colours neuro-secretion 

 purple and chromatin black; some chitinous structures are stained purple. 



The brain and corpora cardiaca 



About 25 neuro-secretory cells (to be called henceforth brain cells) lie in a 

 tight group medially and dorso-posteriorly in the cerebral ganglion (brain). 

 They send axons forwards which then turn ventrally and go back towards 

 the corpora cardiaca (to be abbreviated cc) and perhaps on to the midgut. 



A period spring larvae. 9 larvae collected in February and fully representa- 

 tive of female variation (with weights from 2-5 to 4-7 mg and wing areas 

 from 2-5 to 7-5 x 10-^ sq. mm) had identical brain cells (Fig. la). Their cyto- 

 plasm was tightly packed with purple granules and in many cases this could 

 be traced down the axons. All the cc contained many similar granules. 



168 



