22 THE DEVELOPMENT OF 



mouth an ectodermal nervous thickening extends the length 

 of the thorax and abdomen. A transverse section behind 

 the mouth(fig. 40) shows the ventral cord an unbroken band 

 extending from side to side. 



In F (fig. 43), the cerebral region is much larger, and 

 near the median line three ganglia are to be seen, the boun- 

 daries between them not having as yet been obliterated. 

 These three ganglia unite to form the " brain" of the adult, 

 and represent respectively, o<7, the primitive cerebral or pre- 

 stomial ganglion of the prenauplius condition ; g l the anten- 

 nular and g" the antennal ganglia of the primitive ventral 

 chain. I have not traced out their derivatives in the com- 

 plex brain of the adult nor have I at any time seen traces of 

 theclivision of the first antennal ganglion which Reichenbach 

 describes('86, p.67)as giving rise to the "Vorderehirnan- 

 schvvellung" and '' Seitenhirnanschwellung " of Dietl and 

 Krieger. 



In stage G is noticed for the first time a differentiation 

 of the nervous system into ganglion cells and fibrous sub- 

 stance. I have not traced the processes sufficiently to add 

 anything new to what is known of the processes of his- 

 togenetic alteration, but would call attention to the cells 

 and nuclei labelled "we" in figs. 47, 48, 57, 58 and 59 

 which are undergoing metamorphosis. These nuclei ap- 

 pear much clearer and stain less deeply than their fellows 

 and the protoplasm of the cells as well as that of the nu- 

 clei is becoming more granular and exhibiting a tendency 

 to be arranged in bands, while in some cases the nuclear 

 wall is breaking down, steps in the process of conversion 

 into the neural " Punct-substanz" of Leydig. Fig. 46 

 passes through the cerebral and antennular (g l ) ganglia 

 and the connective uniting them. In fig. 48 is shown the 

 commissure (cw 8 ) connecting the antennular ganglia of the 

 right and left halves of the body, while cm 3 in fig. 48 

 shows the commissure between the antennal 



