No. 3.] 



THE CELL-LINEAGE OF NEREIS. 



429 



Liimbricits (Diagram VI, E) and in a modified fovm by Rhyn- 

 cJielmis and the Hiriidinea, the primary mesob lasts remain in their 

 original position, the mesoblast-bands are parallel to the original 

 lips of the blastopore, and the embryo7iic mesob last-axis persists 

 in the adult. The same is true of the neural axis ; for the 

 neural bands are parallel to the mesoblast-bands, forming with 

 the latter the principal basis of the so-called germ-bands. 



Diagram VI. 



A. Early annelidan gastrula. The mesoblast is shaded. 



B. Horizontal type of the foetal form (^Lumbrictis) . 



C. Vertical type of the larval form {Polyg07-dins, etc.). 



For the evidence on which this statement rests I refer to my 

 paper on Lnmbricus (No. 29) and to the well-known researches 

 of Whitman and Vejdovsky. 



(2) In the second type, represented by the PolychcBta in general 

 (Diagram VI, C), the primary mesoblasts or their eqinvalents are 

 sooner or later carried downwards until they lie approximately at 

 the centre of the lower hemisphere. The mesoblast-bands ai-e 

 therefore at right angles to the lips of the blastopore ; i.e. the 



