Plate 23. 



Stages in the development of the parasitic generation in Pegantna smaragdina, sp. nov. 

 All figures from sections. Figs. 1-7 X 1600; Figs. 8-11 X 900. 



Fig. 1. Two-celled stage ; nurse nucleus (n.u) in process of amitotic division. 



Fig. 2. Four-celled stage ; nurse cell contains two nuclei. 



Fig. 3. A later stage with about twelve blastomeres. The cytoplasm of the nurse en- 

 closes large vacules and it has two nuclei (n.n). 



Fig. 4. Slightly later stage, with about sixteen blastomeres. The nurse nuclei (n.n) are 

 flattened and cap-like. 



Fig. 5. Section through morula stage, lying close to endoderm of parent host. One of the 

 blastomeres is in process of mitosis. No differentiation into ectoderm and 

 endoderm is yet visible. The cytoplasm of the nurse is now thin; (n.n) nurse 

 nucleus. 



Fig. 6. Morula stage, surface view. The nurse nucleus (n.n) covers the embryo like 

 a cap. 



Fig. 7. Section through slightly later stage. The embryo is now in close contact with the 

 endoderm of the parent (en). The central cells of the morula, the future en- 

 doderm, are now divided from the peripheral layer by a thin, but deep staining 

 layer, probably the earliest manifestation of the mesogloea. The cytoplasm 

 of the nurse is now exceedingly thin. 



Figs. 8-11 are of larvae lying free in the gastric cavity of the parent host. 



Fig. 8. Longitudinal section of earliest stage formed free in the gastric cavity of the 

 parent host. Ectoderm (ec) and endoderm (en) are now clearly distinguishable, 

 but there is as yet no trace of gastric cavity. From a specimen stained in 

 borax-carmine. 



Fig. 9. Section through slightly later stage, in which endoderm (en) and ectoderm (ec) 

 are separated by a distinct mesogloea. Ectoderm and endoderm cells now show 

 a difference in size. 



Fig. 10. Section through later stage ; the ectoderm (ec) and endoderm (en) cells show 

 differentiation, the former being small and cubical, and staining deeply; the 

 latter large, chordate, and staining but slightly ; (s.lam) mesogloea. 



Fig. 11. Still later stage, in wliich the differentiation of ectoderm and endoderm cells has 

 progressed even further. The larva is now elongate. 



