368 



4) Concerning the difficult and much discussed question of the 

 origin of this common anläge, my conclusions are as follows: 



a) That it does not arise from the ectoderm is absolutely certain. 

 Throughout its entire development it is widely separated from this 

 membrane and there is not the least evidence either of cell prolifer- 

 ation or of cell migration in any particular part of ectoderm at any 

 time during the development of the blastozooid, excepting where the 

 branchial and atrial openings are going to form. 



b) The question then resolves itself to this: does the anläge arise 

 from the "endoderm" or from the free cells contained in the blood 

 surrounding this latter? During all its earlier stages of development 

 the anläge is in close contact with the "endoderm", but for the most 

 part a line of separation between the two structures can be made out. 

 There are, furthermore, to be found in various parts of the space be- 

 tween the ectoderm and the "endoderm" many cells that are quite 

 similar to those of the developing anläge. 



These two last facts point to an origin of the ganglion and hypo- 

 physis from the free cells of the blood. They are, however, all the 

 evidence in favor of this view that I have been able to get. 



On the other hand in every one of the many youngest stages that 

 1 have studied, I find that the generally distinct line of separation 

 above mentioned, is at some points interrupted, so that an 

 indistinguishable transition from the cells of the "endoderm" to those 

 of the neuro-hypophyseal anläge is to be traced. But again and finally, 

 Ibelievelam able to trace cells in the act of migration 

 from the "endoderm" into the anläge. I therefore conclude 

 that the central nervous system and the hypophosis are derived from 

 the "endoderm". 



5) The simple pericardial vesicle appears very early, about simul- 

 taneously with the gangliohypophyseal anläge, and is at this time 

 closely applied to the wall of the "endodermic" vesicle. I have not, 

 however, been able as yet to satisfy myself as to its origin. But this 

 much is clear: It does not arise, either directly or indirectly in con- 

 nection with the stolonic partition as it is said to do in the bud of 

 Clavelina, nor is there present at any stage the epicardium that exists 

 in Goodsiria and various other Ascidians, notably in Clavelina. 



Naples, Dec. 1, 1894. 



Frommaaoscbe buchdruckerei (Hermaau Fohle) in Jena. 



