ON THE BRAIN OF THE COCKROACH. 353 



forming the inner part of the wall anastomose freely^ so as 

 to form a network of broad fibres, with elongated interspaces 

 having the appearance of cells. These fibres are intimately 

 united with a similar, but much finer, network, which 

 makes up the greatest part of the calicular walls. In the 

 latter portion may be seen rounded transparent areas of very 

 different sizes, and other irregular patches of a darker and 

 granular substance. 



Corpus centrale. — The peculiar laminated arrrangement of 

 nervous matter, described by Dietl in the bee and mole- 

 cricket as a median commissural system, is called by Flogel 

 the central body. This structure is not so clearly defined 

 in my preparation of the cockroach as it is in the two insects 

 just mentioned. In the series of frontal sections (34) 

 from which this description is taken, the lamination of the 

 central granular substance is first seen in the thirteenth 

 from the front (fig. 8 c). Here the granular mass is indis- 

 tinctly divided into four parts, and is surrounded by 

 irregular cells and interlacing fibres ; from the latter fibrous 

 bands are seen passing upwards and outwards, some of 

 which may be traced to the optic nerve. Below the 

 granular mass, the cells are partly divided into groups by 

 dark fibres passing down among them. In the 12th 

 section only a small portion of the granular substance is seen, 

 while the celk and fibres are more abundant and evident. 

 In the 14th section the granular substance is clearly 

 divided into six parts, which occupy nearly the whole width 

 between the trabecules. Below this the cells are beginning 

 to give place to granular matter, and this shows some indica- 

 tion of being divided into plates (fig. 11). Passing to 

 the 19th and 20th sections, we find that in the upper 

 portion the divisions of the granular mass have increased 

 in number to twelve or fourteen, these divisions, however, 

 are not so clearly marked off" as in the more anterior sections. 

 Above this there is a row of very transparent cells, and 

 below there is little else than granular matter and fibres, 

 from among which dark branches pass upwards, and 

 dividing, separate the granular matter into its laminee. In 

 this region fibres are seen passing off" from the sides of the 

 corpus centrale, and arching over the now reduced trahe- 

 cida, extend in the direction of the oesophageal commissures. 

 The divisions of the granular matter are still to be traced 

 in the 22nd and 23rd sections, and continue to occupy 

 as great a width; notwithstanding this, the granular 

 matter has almost entirely given place to cells in the 24th 

 section. Throughout its length, the upper surface of the 



