ECTODERMAL DERIVATIVES 



105 



divided into three pairs of lobes (Fig. 47, lob), the most lateral being the 

 optic lobes (lob.l). In the two median pairs of lobes the neuroblasts 

 (neur) have the typical form of those found in the ventral nerve cords, 

 the daughter cells (gglc) forming the usual ganglion cells whose interlacing 

 fibers represent the neuropile. The neuroblasts degenerate after the 

 formation of the daughter cells. Before the optic lobe is fully differ- 



lob I 



eci.d 



Fig. 48. — Mantis rdigiosa. Cross section of head through developing eye. A-C, 

 successive stages, (am) Amnion, {ect) Ectoderm, {ed. d) Dermatogene cells, {ect. 

 ggl) Gangliogene cells, {eye) Eye plate (disk), {loh) First, second, and third protocerebral 

 lobes, {mes) Mesoderm. {From Vicdlanes.) 



entiated and is still a part of the epidermis, the region may be dis- 

 tinguished by its rather large cells. Although it is generally conceded 

 that no neuroblasts take part in the formation of optic lobes in insects, 

 these larger cells in Mantis are termed " gangliogenes " (i.e., neuroblasts) 

 by Viallanes (1891). Heymons, in his account of the development of 

 Forficula, states that they correspond to neuroblasts, not that they are 

 neuroblasts. 



The development of compound eyes in the paurometabolous insects 

 is brought about by the formation of an eye disk (eye) in the ectodermal 



