No. I.] CONTRIBUTIOiX TO INSECT EMBRYOLOGY. 97 



his attention was concentrated on the structure of the brain. 

 He has observed the degeneration of the gangliogenic cells, or 

 neuroblasts. In a late stage ('90^, p. 301), he says " lis montrent 

 des signes evidents de decrepitude; beaucoup des cellules gang- 

 liogenes ont deja disparu, les autres sont en voie d'atrophie." 



Our knowledge of the median cord cannot be said to have 

 made much advance since this structure was first described by 

 Hatschek ('77). While all writers agree that it originally ex- 

 tends as an uninterrupted structure from the mouth to the 

 anus, there is wide difference of opinion respecting the ultimate 

 fate of its inter- and intraganglionic portions. Hatschek ('77), 

 Tichomiroff ('82), and Korotneff ('85) maintain that the inter- 

 ganglionic portions remain attached to the integument when the 

 nerve-cord is liberated and that they ultimately disappear. 

 Ayers ('84) on the other hand holds that the whole median 

 cord is liberated from the ectoderm, but does not affirm that 

 the interganglionic portions form a constituent part of the 

 ganglia. 



Graber ('9o) has very recently come to a conclusion which 

 differs from the views hitherto advanced. With Ayers he 

 holds that the interganglionic portions of the median cord are 

 delaminated from the ectoderm along with the intraganglionic 

 portions, but he goes further and claims (p. 103) that 

 "das Zellenmaterial des interganglionalen Mittelstranges, 

 zum Theil wenigstens mit den Ganglien vereinigt wird, oder 

 mit anderen Worten, dass eine Vergrosserung des ganglionalen 

 Mitteltheiles auf Kosten des interganglionalen erfolgt." 



As will be inferred from the above descriptive paragraphs, 

 I hold to Hatschek's view that the interganglionic portions 

 of the median cord take no part in the formation of the 

 ganglia but are drawn out from between the connections and 

 constitute a portion of the sternal integument. Graber' s re- 

 searches on this portion of the nerve cord are limited to the 

 Coleoptera and as the insects of this order certainly differ to 

 some extent from the Orthoptera in the formation of the 

 nervous system, I have no grounds for doubting the correctness 

 of his observations. I believe, however, that Ayers' account 

 of the median cord in OEcantJius is open to criticism. After 



