No. 2.] DEVELOPMENT OF MARINE ANNELIDS. 



305 



REFERENCE LETTERS. 



The quadrants of the egg are indicated by the letters a, b, c, and d. The cells 

 at the two poles of the eggs are distinguished by these letters with figures as sub- 

 scripts, e.g., A3, B^, etc., at the vegetative pole, a^.^, b^.^, etc., at the animal pole : 

 for the other cells the figures are written as exponents, e.g., a^-', i^^-^. In general, 

 the upper product of a cell division receives the smaller exponent, thus : 



5 a=-'-' 



I 



J2.2.I 

 ,2.2.2 * 



The following abbreviations are also used : t 



*, landmark, first seen in Fig. 35. 



bp., blastopore. 



eiit, entoderm. 



gl.l., left dorsal umbrellar mucous gland. 



gl.rt., right " " " " 



gl., other umbrellar mucous glands. 



/', /^, P, cf. reference to Fig. 34. 



mem., egg membrane. 



M, mesoderm proteloblast. 



m. m, anterior products of first division of paired mesoblasts. 



MM, paired mesoderm cells, or teloblasts of mesoderm bands. 



mes., mesoderm bands. 



par., paratroch. 



par.v.lft., left ventral paratrochal cell. 



par.v.rt., right " " " 



par.d.lft., left dorsal " " 



par.d.rt., right " " " 



proc, proctodaeum, or anlage of same. 



p.g., polar globules. 



prot., prototroch. 



som.pl., somatic plate. 



stomod., stomodseum. 



*The nomenclature is that of Wilson ^ somewhat modified, p. 230. 



The blue tint is used to distinguish the " cross " and the somatic plate ; brown, 

 the prototroch ; light red, the mesoderm ; the entoderm is stippled. 



t Other abbreviations used but once are explained in the special reference to the 

 figure. For substitution letters, ap^, ap^, etc., see table, p. 236. 



