156 John H. Geroüld. 



n^mu. r. / ventro- lateral neuromuscular organ 



nph nephridium 



nph'po nephridiopore 



nph'st nephrostome 



nu cj sperm nucleus 



mo Ç egg nucleus 



nu. pr'trch nucleus derived from a prototroch cell 



71. V ventral nerve cord 



oc eye spot 



OS mouth 



jiap papilla of an epidermal organ 



prc'd proctodaeum 



])r'trch prototroch. or cells bearing the prototroch (adorai cilia) 



ros rosette 



stm^d stomodaeum 



tab. fipx apical plate 



tab. so somatic plate 



vt yolk granules 



z. r zona radiata (vitelline membrane). 



Plate 4. 



The figures were drawn from sections of eggs that had been fixed 

 hy the following mixtures: Fig. 10, 16 and 19 Heemann's platino-aceto 

 osmic ; Fig. 17, picro-nitric ; the remaining figures, sublimate acetic. The 

 sections were stained with iron-haematoxylin, except that shown in Fig. 1, 

 in which case borax carmine was used. Fig. 1 — 6 and 17 are of Ph. 

 gmddn, the others are of Ph. rnhjare. 



Fig. 1. Ovarian egg, showing an astrosphere. 1460: 1. 



Fig. 2. Egg from the coelom, showing the inner and outer layers 

 of cytoplasm and a thin yolk membrane. 1020 : 1. 



Fig. 3. Chromosomes of the first maturation spindle, as viewed from 

 the side. 2500 : 1. 



Fig. 4. Similar to Fig. 3. 



Fig. 5. Chromosomes of the first maturation spindle, as seen in a 

 cross section of the spindle. 2500 : 1. 



Fig. 6. First maturation spindle. 880 : 1. 



Fig. 7. Late anaphase of the first maturation spindle. Twenty-one 

 minutes after fertilization. 2500 : 1. 



Fig. 8. Budding off of the first polar body. The sperm nucleus is 

 also visible. Twenty-one minutes. 670:1. 



Fig. 9. Reconstruction of the spindle after the formation of the 

 first polar body. Twenty-one minutes. 670 : 1. 



Fig. 10. Second polar spindle and sperm nucleus with enlarged 

 astrosphere near the centre of the egg. Thirty-five minutes. 1580 : 1. 



