OOO I. IKEDA : 



merely by u local dillerciitiatioii of tlic cctoLlastic cells into iiei'- 

 VOU8 elements. The epidermis over l)otli the ganglion (fig. 14. gl.) 

 and the sensory spot (.so.) is strongly ciliated, so that the organs 

 ai'e easily recognizahlc in the living larva. The earliest stage 

 in Avhich I tbnnd the ganglion was a 4-armed larva of type ^1 

 (fig. 40 (/l.). In it, the ganglion consisted of only a few ganglion 

 cells and nerve fibres. 



Although tlie ganglion and some nerves directly ])roceeding 

 from it can l)e detected with tolerable distinctness in the living- 

 specimen on account of their peculiar refractivity, the peripheral 

 nerves are as a o-eneral rule so verv line and delicate, that thev 

 can not be satisfactorily made out by means of any ordinary 

 process. With fair success I have had recourse to vital staining 

 with methyl-blue. Larva' of type i> have been principally em- 

 ployed for this purpose. They are left for about l'")-20 minutes 

 in a weak solution of methyl-ldue in sea water and immediately 

 afterwards treatetl with ammonium molybdate. Sometimes, I have 

 made supplementary ol)servations on larvœ lyiug alive in the 

 methyl-blue solution under the cover glass, but this can l»e con- 

 tinued for only a slujrt time, since a general o\'erstaining of other 

 tissues soon takes ])lace. 



Fig. GO (V^' shows the dorsal view of the anterior half of a 

 larva of ty])e JJ, which was treated in the abcjve way. The nerves 

 are shown in blue. The results obtained as to their distribution 

 dilfer in many important points from those (»btained by MasïEK- 

 MAN. AVhcther this dilferen<'e is due to the technique or is 

 actually existant in the species studied, is diilicult to ascertain. 



* As the larva sliown in tliis figure was compressed by the eover-glass, the rim of the liooil 

 wliieli appears like its free margin is in reality tlie line along Avliieli tlie hood was bent and 

 reOected over l)y pressure. Tlie line drawn close to the peripheral dots in blue rej)resents the 

 true edge of the Jiooil. 



