108 H. H. NEWMAN. 



made on May 20 shows the full range of diversity and will serve 

 to illustrate all of the points of interest. As the time element is 

 of prime importance in this study it is necessary to give readers 

 as a norm for purposes of comparison a time schedule of the 

 development of the normally fertilized Asterina. 



TIME SCHEDULE OF THE DEVELOPMENT OF NORMALLY FERTILIZED EGGS OF 



ASTERINA. 



Hours after Shedding. Condition of Maturated and Fertilized Eggs and Embryos. 



2*4 Fertilization membranes formed on majority of matured eggs. 



3*^ Cleavage beginning. 



5 Cleavage taking place in all fertilized eggs, a few 4 and 8 



cell stages. 



7 Many stages as advanced at 32 -f- cells. 



9 Most of eggs in early blastula stages, but there are a good 



many eggs without membranes, in early cleavage stages. 

 These are probably parthenogenetic. 



25 Two distinct types of larvae present : the great majority being 



typical gastrulae, swimming up near the surface of the dish, 

 and capable of being readily pipetted off; a small minority 

 of living larvae variously abnormal and swimming at or 

 near the bottom. These latter are probably, though not 

 certainly, parthenogenetic. 



49 Normal larvae, early bipennariae, forming enterocoel pouches. 



73 Bipennariae with well-defined ciliated bands. 



96 Advanced bipennarise with mouth, oesophagus, stomach, in- 

 testine, anterior and posterior enterocoels, waterpore, etc. 



TIME SCHEDULE OF THE DEVELOPMENT OF PARTHENOGENETIC EGGS OF ASTERINA. 



No. of Ex- Hours after 

 periment. Shedding. Condition of Maturated Eggs or of Developing Embryos. 



1 7 No membranes and no cleavage. 



9 About i per cent, of eggs show distinct membranes, 



no cleavage. 



24 About y 2 of i per cent, swimming blastulae, all sub- 

 normal in appearance, irregular in shape or solid. 

 About 2 per cent, early cleavage stages (2 and 4 

 cell stages). 

 48 All larvae and cleavage stages undergoing cytolysis. 



II 7 No membranes and no cleavage. 



9 No membranes and no cleavage. 



24 No larvae nor cleavage. 



Ill >y 2 No membranes and no cleavage. 



8% No membranes, but about i l /2 per cent, of cleavage 



stages, mostly fairly regular 2 and 4 cell stages. 

 25 Nearly i per cent, blastulae, mostly solid and mo- 

 tionless. 



