536 DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



clear. The corneal lamina is uniformly thin throughout its whole 

 extent, except where the sucker of the larva originates. From 

 it also develop the internal cellular lining of the central canal, 

 the external cellular coat of the animal, and the cellular invest- 

 ment of all the glands connected with that coat. I have more- 

 over found that the nervous lamina, even at the earliest period, is 

 thickened in the region where the brain subsequently makes 

 its appearance. Proceeding outwards from this point, it be- 

 comes gradually attenuated towards the caudal extremity 

 (yolk plug), and rather quickly in all other directions. 



No special thickening exists for the rudiment of the retina, 

 since this, as is well known, is developed from the brain (by a 

 process of eversion). Special thickenings however occur for 

 the olfactory, auditory, and gustatory organs.* I have no 

 remark to make in regard to the rudiment of the tactile organ. 

 J can only point out that the nerve lamina, like the corneal 

 lamina, surrounds the entire periphery, and the relation that 

 exists between the peripheric expansion and the tactile organ 

 still remains, therefore, to be investigated. 



Notwithstanding the positive statements of Remak, I cannot 

 consider it to be satisfactorily established that nervous struc- 

 tures can also be developed from the middle germinal lamina. 

 The subject still demands further careful investigation. Obser- 

 vations made upon the tail of the larva of the Frog render it 

 probable that the peripheric nerves proceeding from the axis 

 to the periphery originally project as masses of protoplasm. 

 Wherever, however, such protoplasmic masses occur, they may 

 also develop cellular elements in their course and in their 

 interior. As long as this theoretical consideration is not 

 opposed by precise observations, we cannot regard this impor- 

 tant question as settled in the sense held by Remak. 



The muscular and connective-tissue substances originate from 

 the middle germinal laminae. This is so readily seen, that, 

 notwithstanding the authority of those who deny it, I shall 

 not enter into any discussion respecting it. In the first place, 

 the chorda belongs to the connective-tissue substances. The 



* See the treatises of Schenk and Torok in the Wiener Sitzungsberichte, 

 Bande 1. and liv. 



