1 84 WILSOAT. ' [Vol. I. 



median line, as shown in Figs, i and 2. At the extreme 

 posterior end lie the two mesoblasts {M) in contact with each 

 other at the median Hne. Two others {N) are placed on either 

 side the median line at a considerable distance anterior to the 

 mesoblasts. A third pair {Np) lie, one on either side, a short 

 distance behind and lateral to the second pair, and a fourth pair 

 {X) are found just outside the last. 



Each of the eight teloblasts gives rise to a row of cells, at 

 first single, that extends forwards between the ectoblast and 

 entoblast. The rows proceeding from the mesoblasts soon widen 

 into a pair of broad mesoblastic plates that form the greater 

 part of the germ-bands and ultimately give rise to the dissepi- 

 ments, muscles, vessels, and, as I believe, to the setigerous 

 glands. The six remaining rows lie between the mesoblastic 

 bands and the ectoblast, but are intimately related with the ecto- 

 blast. The two inner rows (r^ Figs, i, 2, 6), arising from 

 the anterior pair of teloblasts, give rise to the corresponding 

 halves of the ventral nerve-cord, and the large cells are, there- 

 fore, neuroblastSy precisely as in Clcpsine. The adjoining rows 

 (r^, Figs. I, 2, 7) furnish the basis of the nephridia, and the 

 third pair of teloblasts {Np^ Fig. i) are, therefore, nephroblasts 

 (of which Whitman describes two pairs in Clepsine). The 

 fourth or outer row (r^) apparently gives rise to a solid band of 

 cells (,r. Fig. 6) that lies between the nephridia and the outer 

 setigerous glands, and may be followed to the anterior end of 

 the body. I have not yet succeeded in determining the ultimate 

 fate of this structure. The arrangement just described persists 

 unaltered for a considerable period, and in its main features may 

 be recognized in embryos eight or ten millimetres long, and 

 nearly ready to hatch. As development proceeds, however, the 

 six anterior teloblasts gradually lose their prominence, and finally 

 can no longer be distinguished, and at the same time the corre- 

 sponding cell-rows become more than one cell wide throughout 

 their whole length. The mesoblasts persist until a very late 

 stage. 



It is evident from the foregoing account that the germ-bands 

 of Ltimbricus, in one species at least, are closely similar to those 

 of Clepsine. As in the Hirudinea generally, each germ-band 

 may be said to consist of three strata of cells, viz.: (i) the 

 ectoblast, (2) the three rows of cells produced by the three 



