No. 2.] DEVELOPMENT OF MARINE ANNELIDS. 23 1 



(i) Instead of designating cells of several successive genera- 

 tions by the same letters, e.g., the " macromeres " A, B, C, D, 

 I have used subscripts, thus : A, A„ A^, etc. (2) Instead of 

 naming the daughter cells sometimes from their relative posi- 

 tion and sometimes from their relative size, I have named them 

 uniformly with respect to their relative positioji, giving the cell 



Fig. I. — Diagrams of egg with circumscribed loxodromic curves, a-b, axis. The curve in A 

 represents the general direction of the cleavage furrows in right oblique cleavage ; in B that of 

 the furrows in left oblique cleavage. 



nearer the vegetative pole the larger exponent. For example, 

 a" divides into «"' and «°■^ and the latter is nearer the vegeta- 

 tive pole. 



This nomenclature is employed purely as an instrument of 

 convenience, and I do not thereby commit myself to any 

 implied theory of development. 



When the cleavage plane of a dividing cell takes the general 

 direction of a loxodromic curve described about the Qgg in the 

 direction indicated in text Fig. I, A, the cleavage is designated 

 as right oblique ; when in the direction of the curve in Fig. I, 

 B, as left oblique. Similarly, we may speak of vertical and 

 horizontal cleavages, when the furrow takes the direction of 

 the meridian, or one at right angles to it. 



I. Cleavage to 64 Cells. 



The normal fertilized egg of Amphitrite is nearly spherical 

 and about lOO/tt in diameter, although there is considerable 

 individual variation. It is enclosed in a much-wrinkled mem- 



