THE EMBRYOLOGY OF THE HONEY BEE 125 



FIG. 47. Transverse sections through the ventral ectoderm of embryos 

 of the grasshopper, Xiphidium. A, early stage, showing segregation of the 

 neuroblasts (Nbl) ; B, late stage, showing the neuroblasts and their pro- 

 ducts, the ganglion cells (GngC). From Wheeler (1893). 



gions the neural groove remains intact as hypodermis, the neural 

 ridges here forming the connectives. 



The histogenesis of the neurogenic tissue constituting the neural 

 ridges and neural groove has been studied by several investigators, 

 but Wheeler (1891, 1893) was the first to give a complete and 

 consistent account of this process, as observed in the grasshopper 

 Xiphidium. The essential features of Wheeler's results have 

 since been confirmed by a number of investigators of the Orthop- 

 tera and also of other orders, among these are Heymons (1895) 

 for the Dermaptera and Orthoptera, Carriere and Burger (1897) 

 for the mason bee, and Lecaillon (1898) for the beetle Clytra. 

 Wheeler's account is briefly as follows : 



At a stage soon after the completion of the formation of the 

 germ layers the ventral ectoderm of the embryo is seen to consist 

 of two different kinds of cells; a small number of large pale 

 cells with vesicular nuclei, and a large number of smaller cells 



