202 



Balfoue gives a stage between J and K as the first time any thicken- 

 ings are seen, but as his observations seem to relate to Pristiurus 

 or Scyllium embryos, any comparisons can hardly be made. Ziegler 

 gives the commencement of the involution of the organ as between 

 J and JST, which agrees with my own observations. 



Fig. 1 shews the median longitudinal section through the head 

 of an embryo in stage H. At the foremost situated point of the 

 head the neuroporus is seen still open but on the verge of closing 

 and the division of the brain into different lobes has commenced. 



A little laterally of the neuroporus the thickenings which repre- 

 sent the first indications of an olfactory organ are found and Fig. 2 

 shews a longitudinal section there-from. 



This is the relative position in which van Wijhe (3) has found 



Fig. 1. Median longitudinal section through an embryo of Torpedo ocellata, Stage 

 G.-B. 120/1. 



The figures are drawn with the Abbe Camera Lenses 16,8 or 4 mm and Comp. Oc. 4 

 by Zeiss. 



Reference letters in above. 

 Ajp. Neuroporus. 01. O, olfactory organ. Ec. ectoderm. Nc. connecting cells. 

 01. L. olfactory lobe. 01. B. olfactory bulb. 



