PLATE C. 



Embryology of Phalangella flabellata. 

 Explanation of lettering. 

 Uj Cavity of the body. I, Cavity of the mantle. 



h, Digestive cavity. m, Mantle, 



c. Mouth of the gastrula. n, Tentacles. 



dy Exoderm. o, Endocyst. 



€y Endoderm. p, Polypide. 



/, Oral face. r, Rectum. 



^, Aboral mesoderm. x, Crown. 



ky Aboral face. z, " Zone anhiste." 



Fig. 1. Cell greatly enlarged. 



Fig. 2. Cell divided in two, still adhering to the endocyst. 

 Fig. 3. Morula. 



Figs. 4, 5. Beginning and enlargement of the cavity of segmentation. 

 Fig. 6. Blastula. 

 Figs. Y, 8, 9. Gastrula in different stages of formation, fig. 8 being a 



vertical section. 

 Fig. 10. A section, showing the appearance of the median swelling, 



which represents the crown. 

 Figs. 11, 12. Development of the median swelling, which at first 

 (fig. 10) is near the oral face, approaching the middle 

 (fig. 11), and afterwards nearing the aboral face (fig. 12). 

 The same figures show the formation of the mesoderm •^, 

 between the aboral face and the posterior walls of the 

 intestine. 

 Fig. 13. Showing a more developed state. 

 Fig. 14. A free embryo, vertical section. 

 Fig. 16. An exterior view of the, same. 



Fig. 16. First stage of fixation, composed of an internal pyriform 

 mass, and an external layer spread over, and following all 

 the contours of the internal mass. Between the two are 

 shown the fatty globules. 

 Fig. 17. The external layer has separated from the internal mass, and 

 has formed a discoidal sac, in which is easily distinguished 

 the endocyst (e), the ectocyst (/i), and the "zone anhiste" 

 [z). Internally are shown the fatty globules and the pyri- 

 form mass, which now begins to show the rudiments of a 

 polypide. 



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