Plate I 



All of the figures of this and the succeeding plates were drawn from parthenogenetic material, with 

 the aid of the camera. The drawings were made under a magnification of looo diameters, except Figs. 

 5-14, as well as Fig. 16, in which the magnification was 700 diameters. The dotted line, which is drawn 

 in many of the drawings surrounding the nucleus or mitotic figure, encloses the yolk-free area. 



All figures are from living material, except 2 and 3 



Fig. I Living egg, showing delicate protoplasmic threads extending from the surface of the egg to 

 the membrane, and also multiple polar bodies. 



Fig. 2 Section of full-grown oocyte immediately after treatment with acid but before breaking down 

 of germinal vesicle; the membrane, which was present, is not represented. 



Fig. 3 Section of egg in which the germinal vesicle has migrated to animal-pole after acid-treatment. 



Fig. 4 Living egg showing three polar bodies; the figure was drawn immediately after the division 

 of the first polar body. 



Figs. 5-8 Two, four, eight and sixteen-cell stages drawn from living eggs. 



Fig. 9 Young HCl trochophore, 15 hours old, showing apical flagella, cilia of prototroch and 

 blastopore bl. 



Fig. 10 HNO3 trochophore, 36 hours old, showing the larger cilia on upper and lower border of 

 prototroch and the mouth mo; the cavities of stomach st, and intestine in, are seen at a deeper level. 



Figs. 11-12 Young trochophores, showing abnormal ciliation; in the former, short cilia cover the 

 entire pre-trochal region, while the latter lacks the apical flagella. 



Fig. 13 Abnormal embryo, in which the cilia have failed to puncture the membrane tnb, and are 

 pressed down by latter. 



Fig. 14 Abnormal 3-cell stage, formed at second cleavage. 



