88 WHEELER. [Vol. VIII. 



sends out a cytoplasmic process which soon ramifies. The mass 

 of fibres thus formed increases in size very probably by the addi- 

 tion of further ramifications till the Punktsubstanz is definitely 

 established as a scarcely stainable body, lying on either side of 

 the median line in the deepest portion of the lateral cord (Fig. 

 27, p.s) In its earliest stages the formation of the substance 

 is easily followed, but very soon the felted fibres become too 

 dense for analysis by ordinary methods of investigation. It is 

 only after a distinct mass is formed in either half of a ganglion 

 that the longitudinal commissures, or connectives as they are 

 best called, make their appearance, and unite the hitherto iso- 

 lated centres in two longitudinal series. Very soon the trans- 

 verse commissures, or commissures proper, of which XipJiidiimi^ 

 like all other insects, has two in each segment, make their 

 appearance. The daughter-cells of the median cord neuroblasts 

 take no part in the formation of the anterior commissure. 

 Whether they contribute fibres to the posterior commissure or 

 not, I must for the present leave undecided. I have seen no 

 evidence in the median cord of a distinct and isolated Punkt- 

 substanz centre, such as is described and figured by Graber for 

 some Coleoptera (('90) PI. V, Fig. 66). I deem it more probable 

 that in XipJiidiiim the commissures arise wholly from the 

 Punktsubstanz masses of the lateral cords. Both commissures 

 are distinctly seen in cross section in Fig. 29. 



The connectives and commissures incompletely divide the 

 cellular portion of each ganglion into five parts, — two lying 

 laterad to the connectives and a median series of three smaller 

 portions separated from one another by the two commissures. 

 The former may be called lateral gangliomeres, and the three 

 median portions respectively the anterior, central, and poste- 

 rior gangliomere.i Of the median divisions the posterior is 

 distinctly the largest from the first. This is due to its being 

 formed in great part by the progeny of the median neuroblast, 

 whereas the anterior and central gangliomeres consist of a 

 comparatively small number of cells, contributed by the lateral 

 neuroblasts. 



1 These are equivalent to Graber's laterale Zellenlager, vorderes, centrales, and 

 hinteres Medianlager. 



