No. 2.] DEVELOPMENT OF MARINE ANNELIDS. 273 



cross-furrows, one at the animal and one at the vegetative 

 pole, which, instead of being at right angles to each other, 

 are parallel. The eight cells divide in the usual direction 

 and form a i6-cell stage (Figs. 122, 123), in which one of the 

 apical cells d^.^, is remarkably large, while its sister cell, <f '■', 

 trochoblast, is no larger than a^'^, b^'^, or <:'■'. In other respects 

 the i6-cell stage is like that of Amphitrite (cf. Figs. 8-122, 

 11-123). 



The nearly synchronous cleavage of all these cells gives us the 

 32-cell stage (Fig. 124). Every cell is located as in Aviphitrite, 

 and their relative size is the same with two exceptions : (T""^ 

 receives the extra material bequeathed by the cell d^ of the 

 8-cell stage, and the four apical cells are of about the same 

 size, — in Amphitrite the two dorsal ones are the larger. 



Every one of the thirty-two cells divides obliquely to the left, 

 but not synchronously. Already (Fig. 124) three of the cells 

 have spindles, while the others are in the so-called resting stage. 

 The familiar rosette is formed in the typical fashion, and most 

 of the other divisions take place as indicated in the remaining 

 figures by spindles or arrows (Figs. 124-130). On account of 

 the regularity of the cleavage and its resemblance to that of 

 Amphitrite, I thought it unnecessary to introduce more figures. 



The division of the primary trochoblasts, colored brown, may 

 be seen in Figs. 125-128; the position of the secondary trocho- 

 blasts and of c^'^'^' and t""''"' in Fig. 132; the mesoderm cells, the 

 above-mentioned rosette, and the primary cross-cells in Figs. 

 126-13 1. 



An actual 64-cell stage does not occur in Chcetoptems, owing 

 to the precocious division of certain cells. Soon after the 

 rosette cells are formed, they ingest the polar globules just as 

 do the apical cells oi Lepidonotus at an earlier period (Figs. 127, 

 131, 132, p. 266). 



I have carried the cell lineage little beyond what may be 

 called the ideal 64-cell stage, but some of the next divisions 

 are of great interest. The primitive cross-cells (colored blue 

 in figures), although in origin and in position exactly like those 

 in Amphitrite, divide strictly according to the rule of alternating 

 cleavage, and do not form the cross (Fig. 131). They usually 



