i6o 



WHITMAN. 



[Vol. I. 



.9 



Tru vph' n^ Tipli' 



Diag. 9. — A diagrammatic surface-view of the neuro-nephric stratum at the pos- 

 terior end of the nearly completed germ-bands. 



n, neural rows; « 3, neuroblasts; «/^, nephridial rows; «//ii5, nephroblasts; m', 

 lateral rows. 



granules of the cells, is strengthened by the action of osmic 

 acid, and thus becomes a most important aid in determining the 

 fate of the cell-rows. 



Tracing the nephridial rows forward in a surface-preparation 

 (Fig. 8, PI. v.), we find each represented behind by a line 

 of single cells ; towards the middle, they become double or 

 triple, while still maintaining the same diameter ; near the be- 

 ginning of the anterior third, the two rows blend ; and here 

 outlines appear, at first shadowy, then more distinct as we 

 advance, cutting the rows into quadrangular plates with 

 rounded angles. The formation of the nephric plates pro- 

 gresses from the cephalic end backwards, keeping exact pace 

 with the metameric division of the embryo. Thus the basis is 

 laid for a pair of nephridia in each somite, although only sixteen 

 pairs are retained in the adult. The details of the process by 

 which these plates are converted into the nephridial organs I 

 have not attempted to follow. It is a point, however, which is 

 worthy of a most careful study. 



