No. I.] THE GERM-BANDS OF LUMBRICUS. 1 85 



anterior teloblasts, and (3) the mesoblastic band, which lies in 

 contact with the entoblast. The second of these layers is, how- 

 ever, intimately related with the ectoblast, and, as will appear 

 farther on, is derived from it. 



II. The Nerve-cord. 



The neuroblasts fit closely into the ectoblast (TV., Fig. 5), and 

 in some cases unquestionably extend to the outer surface, as may 

 be seen with especial clearness when they are rounded and 

 swollen at the time of division. The position of the amphiaster 

 visible at this time demonstrates the fact that cells are 

 added to the neural row at its posterior end by division of the 

 neuroblast ; and my preparations indicate that all the neural 

 cells have a like origin. Although the neural rows are closely 

 applied to the ectoblast, they are always separated from it by a 

 distinct line (Figs. 3, 7), and they assume a clear red color with 

 borax-carmine, while the ectoblast cells are stained brownish 

 red. In late stages, after disappearance of the neuroblasts, the 

 neural rows, now several cells wide, still appear to increase in 

 length by division of the cells at their posterior ends, and not 

 by proliferation of the ectoblast (Fig. 7). 



The ventral nerve-cord is formed by the gradual concrescence 

 of the neural rows in the median line (Fig. 6). There is no in- 

 dication that the subjacent ectoblast takes part in the formation 

 of the cord, and, so far as L. olidus is concerned, Hatschek's 

 account of the matter is certainly incorrect.^ No invagination 

 from the exterior takes place ; no medullary canal is formed, 

 and the continuity of the ectoblast across the median line is 

 never broken. Unless the development of L. riibelliis differs 

 very widely from that of L. olidus, Hatschek has mistaken the 

 narrow angular interval between the converging halves of the 

 cord for an evidence of invagination. 



III. The Nephridia. 



The foregoing account of the neuroblasts and the neural 

 rows will apply, mutatis mutandis, to the nephroblasts and the 

 nephridial rows (compare Figs. 4 and 5). Anteriorly these 

 rows are always clearly defined at the sides by delicate bundles 



» Sitzungsb. d. k. Akad. Wien. Ixxiv. 1876. 



