conclusion :';hich Seeliger drev/, from purely theoretical con- 

 siderations, concerning tne origin of tnese structures in 

 Clav elina is also true of Peroph ora viridis. I shall try 

 to show tnat tnere is every reason to believe that tne dorsal 

 tube and ganglion are derived from .'7ies oder:nal cells . 



The dorsal tube is formed long before the ganglion , 

 and the rudiment from which it v/ill arise is first indicated 

 just after the collection of cells v/hich is to produce the 

 pericardiam makes its appearance. 'Vhen the difference in 

 thickness between the right side and the rest of the vesicle 

 is becoming apparent, hence at a time --.vhen tne rotation is 

 about beginning, in the anterior portion of the bud, a little 

 to the left of the median dorsal line, there is seen an ir- 

 regular elongated patch of cells very loosely grouped togeth- 

 er and lying on the outer surface of the inner vesicle, Pig. 

 28, d^.t. The free mesodermal cells in the space between the 

 ectoderm and endoderm are especially numerous in this region, 

 and are closely associated with the collection of cells ad- 

 hering to the vesicle. Although I have examined my sections 

 with the greatest care under a ■'"/12 oil-i.'nmersion lens, from 

 the very first appearance of the rudiment, I have failed to 

 find any indication of cell-migration from the endodermal 

 wall, and therefore cannot confirm Hitter's statement (I.e. 

 page 368) that an "indistinguishable transition from the 

 cells of the 'endoderm' to those of the neuro-hypophyseal 

 anlage is to be traced", and also that cells can be found 

 "in the act of migrating from the "endoderm" into the anlage." 



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