22 THE DEVELOPMENT OF 



mouth an ectodermal nervous thickening exteiids tlie length 

 of the thorax and abdomen. A transverse section behind 

 the inoutli(fig. 40)shows the ventral cord an nnbroken 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 betvveen them not having as yet been obliterated. 

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

 and represent respectively , o^,the primitive cerebral or pre- 

 stomial ganglion of the prenauplius condition ; g^ 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 

 thedivision of the first antennal ganglion wliich Reichenbach 

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

 schwelhmg" and " Seitenhirnanschwellung " of Dietl and 

 Krieger. 



In staofe 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 " 7ic" in iigs. 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 protophism of the cells as well as that of the nu- 

 clei is becoming more granulär and exhibitiug 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^) ganglia 

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

 commissure {cm^) connecting the antennular ganglia of the 

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

 shou^s the commissure betwccn Ihc antennal i!:ani>lia. 



