OTIC AND OPTIC PRIMORDIA IN MAN Aik 
the mitotic figure develops, most of the cytoplasm flows up 
around it. The resemblance of the dividing cells to the germinal 
cells of the central nervous system is obvious and they occupy 
the same relative position in the epithelium. The brush border 
appears over the central cells of the otic plate, and in this sec- 
tion resembles a band of short exceedingly delicate cilia. At 
other levels it looks more like a granular exudate. This is prob- 
ably not due to inadequate fixation, as the specimen came from 
an unruptured tubal pregnancy with a strikingly normal appear- 
Fig. 7 A section through the middle of the otic plate of the eleven-somite 
embryo H637 (Univ. of Chicago Coll.). Camera drawing with 2-mm. Zeiss 
apochromate and comp. ocular 2 at 1000 diameters and reduced one-half in repro- 
duction. The wavy line below at the right marks the external boundary of the 
neural tube. There is no mesenchyme between it and the otic plate. 
ing implantation site and was immediately opened and placed in 
Zenker stock solution. That the embryo was normal is very 
probable. There were no immediate symptoms clinically ex- 
cept a lapsed menstrual period. Unfortunately for the embryo, 
it was cut and folded in the process of opening, but cytologically 
it is excellent. The plate cells show a well-developed internal 
reticular apparatus (‘canalicular apparatus’) which has not been 
detected in any other cells of the ectoderm at this stage. It 
appears as a series of clear spaces in the cytoplasm. It will be 
recalled that Ramén y Cajal (’12) found the internal reticular 
