270 MEAD. [Vol. XIII. 



The eggs of Harmothoe sp. are slightly smaller and clearer 

 than those of LepidonotuSy and develop in almost exactly the 

 same manner. I have tried to obtain hybrids between these 

 species, but without success. 



D. SCOLECOLEPIS VIRIDIS verrill. 



The breeding season of this species is nearly over by the first 

 of May. The eggs are deposited inside the sand-tubes in which 

 the females live. They are of medium size, and of bright 

 yellow color. The membrane does not adhere so closely as in 

 some other species (Fig. 105). The first division is unequal. 

 At the next division, the smaller cell very often divides first. 

 In the 4-cell stage D has a relative size even larger than usual. 

 The four cells divide almost synchronously into eight, in the 

 usual right-oblique direction. The peculiarity of the 8-cell 

 stage is that the apical cells, a.^, ^„ c^, d^, are very small and 

 perfectly transparent, while the vegetative cells are very large 

 and perfectly opaque. 



The four lower cells divide again, and the lower products 

 of this division, A^, B^, C^, D^, are all opaque. Of the four 

 upper products, a", b'^, and c^ are transparent and comparatively 

 small, while d^ (somatoblast in other forms) is opaque and of 

 enormous size. Very soon the four apical cells, a^, b^, c^, d^, 

 divide in the usual left-oblique direction (Figs. 110-113). 



Though all the previous divisions and the present positions 

 of the cells are the same as in Lepidonotiis at the i6-cell stage, 

 the relative size of the blastomeres presents a remarkable con- 

 trast (Fig. 112). The cells colored brown in Figs. 112 and 114 

 correspond in origin to the primary trochoblasts of other forms, 

 — AmpJutrite, Clymenella, and Nereis. 



Notwithstanding the great differences in the size and in the 

 constitution of these sixteen cells, they all divide again almost 

 simultaneously, with the exception of the trochoblasts «'■^ <^'"^, 

 c'"^, /^''^ the direction alternating as usual with that of the 

 previous division. The failure of the primary trochoblasts to 

 divide with the other cells prevents the egg from actually at- 

 taining the typical 32-cell stage. The difference between the 

 relative size of the cells of the d quadrant and that of the corre- 



