PLATE IX. Fig. 16. The ectoderm is at the top, the endoderm at the 

 bottom and separated from each other by mesoglea. A rather robust process 

 passes from an endodermal cell into the mesoglea. 



Fig. 17. Longitudinal section of the junction of two muscle fibers in the 

 ectoderm. The alternating light and dark densities on adjacent cell mem- 

 branes yield a desmosome-like effect. Muscle filaments do not pass from 

 one cell to the other. 



Fig. 18. Flagella in the lumen of the hypostome surrounded by a mem- 

 brane and exhibiting the characteristic pattern of filaments. 



24 



