60 CHARLES BROOKOVER 



not been figured. At this time, which is thirty-four hours before 

 hatching each of the paired placodes is still connected with the 

 ectoderm at a point between the sucking disks, although by a 

 more slender cord of cells than was the case in the earlier stage 

 described. But the points where these two cords of cells reach 

 the ectoderm adjacent to and between the two halves of the 

 sucking disk, are now removed farther laterally from each other. 

 From a position midway between the two halves of these two 

 paired placodal connections with the roof of the mouth, there is 

 still a strand of cells extending from the ectoderm to the anterior 

 ventral edge of the tip of the neural tube. This cord of cells is 

 largest near the neural tube. There is no appreciable increase 

 in the size of the connection of the paired placodes with the 

 brain over the previous stage described. A slight indentation of 

 the cuticular ectoderm shows where the external opening of the 

 nasal sac will appear later. The embryos showed slight motions 

 at this age. 



About twelve hours later than the last stage, or some twenty- 

 two hours before hatching, there is no unpaired nasal placode 

 nor any evidence of a cord of cells from the roof of the mouth 

 to the brain wall at its anterior end. The paired placodes in 

 one or two preparations of this stage have shown a slight elonga- 

 tion into a point forward just beneath the ectoderm. The nasal 

 placodes, as well as the anterior end of the neural tube, are 

 farther removed from the anterior end of the snout than was 

 the case earlier. At this time there appears to be a fibrous con- 

 nection between the olfactory capsules and the brain (fig. 2). 

 Whether this connection is protoplasmic or is composed of true 

 neurofibrils such as those described by Paton ('07), was not de- 

 termined, as the method of Bielschowsky which was tried, did not 

 differentiate any fibers in young or embryonic Amia. The con- 

 nection is quite slender, as it is seen in only two sections, and is 

 in consequence not more than twelve micra in thickness. A 

 very few cells of the placode near the place of origin of the fibers 

 are slightly larger than the others at this age. The distance from 

 the placode to the outer brain wall is almost nothing at this age 

 and there are no nuclei in the course of the olfactory nerve. 



