mi 



I atarted. by asoerlaiiiing whether there were developmental stages 

 in which liie pnlaritj of tlie ciliated cell is reversible, that is sitages 

 in which the ciliated cells can be forced to move in a direction 

 other than the normal. 



After circumcision with line glass-needles patches of ectoderm 

 were detached liüm their sublayer and after a rotation of 180° — 90° 

 brought again to coalescence. After the wounds thus made were 

 healed, which occurred in a marvellously short time, the direction 

 of the ciliiUT movemenl was determined by examining the larvae 

 in water in whicii granules of carmine had been suspended. A 

 disadvantage of this procedure appeared to be thai Ihe borders of 

 the wound are soon altogether invisible, so that the extent of the 

 reversed regions cannot be traced oul. For this reason I used the 

 method adopted by W. Voor '), who interchanged ectoderm patches 

 of larvae stained vitally ami those of nonsfained larvae. After it 

 had tirsi been ascertained thai vital staining with Nile-blue sulphate 

 did not atï'ect the ciliai-y action, I stained one of two larvae of the 

 .same age-period, and the other I did not. Of these two larvae frag- 

 ments of ectoderm of a very well-delined shape and of the same 

 size were excised and interchanged. In the transplantates the colour 

 remains very well localized, it does not diffuse and enables us to 

 recognize the contour of the implanlate for many days still. More- 

 over, the shape of the implantate is indicative of its original position, 

 consequently of the direction of the currents produced by the ciliary 

 movemeni under noi'tnal circumstances. 1 shall not give an account 

 of the various experiments, but I will describe briefly the final result 

 of all of them. 



It became evident that when a ciliated cell has once begun to 

 vibrate it cannot be made to move in another direction. Patches of 

 ectoderm being implanted in the wrong direction persisted to move 

 in their original direction for days, nay, even till the ciliated cells 

 had disappeai'ed from the epidermis. Even befoie the ciliary move- 

 ment has begun, its direction has already been established. When 

 ectoderm fragments are reversed 180° before the ciliary movement 

 begins, the ciliated cells will afterwards reveal a vibration opposite 

 to that under normal circumstances. The youngest stages of develop- 

 ment, however, are excepted in this respect, as it appeared that 

 in blaslulae and in incipient gastru la-stages the blastula-i'oof resp. 

 ectoderm-patches can be reversed, without affecting the direction of 

 the movement, when afterwai'ds the larvae begin their ciliary action. 



1) W. VoGT. Verhandl. deutsch. zoolog. Gesellscli. Bnd. 27. Sept. 1922. p. 4!*. 



