ILLUSTRATIONS. 85 



PLATE IV. 



(All figures of Tropiornetra carinata. All X290.) 



FIG. 1. Longitudinal, oblique-frontal section through an embryo 25 hours old, showing the first rudiment 

 of the chambered organ in the shape of a process from the anterior end of the right enterocoel. 

 (The ectoderm of the anterior end of the section figured was destroyed; that has been restored 

 from another series of sections through an embryo of exactly the same age and stage of 

 development.) 



FIG. 2. Sagittal section of an embryo 25 hours old. The large cavity of the left (posterior) enteroccel is 

 probably a feature due to the preservation. The hydroccel is now nearly ring-shaped, which 

 accounts for its appearing as two separate spaces in the section. The character of the ectoderm 

 is to be noted the secernment of intercellular substance is in full progress, and a distinct 

 limit between the ectoderm and the mesenchyme is no longer to be seen. The epithelium of 

 the ccelomic vesicles has begun to assume an endothelial character. 



FIGS. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. From a series of transverse sections through an embryo 25 hours old. 

 Between figures 3 and 4 there are 5 sections, between figures 4 and 5 only one, while figure 6 

 follows directly after 5, and 7 directly after 6; there is one section between 7 and 8, while 9 

 follows directly after 8; between 9 and 10 there is one section and the same between 10 and 11, 

 and finally there are 2 sections between 11 and 12. The series gives the relation between the 

 crelomic vesicles, the entoderm and hydroccel, while the parietal canal could not be made out 

 in this series. All the figures are drawn in the same orientation, the ventral side down, the 

 dorsal side upwards. 



FIGS. 13, 14. Longitudinal, sagittal sections through an embryo 40 hours old. The sections are somewhat 



oblique. The two sections figured are separated from one another by 5 sections. X290. 

 Figuie 13 shows the vestibulary invagination; the suctorial disk is fairly distinct. 

 In figure 14 is seen the prolongation from the chambered organ through the stalk-joints. The 

 parietal canal is distinct in this and the two following sections, continuing backwards as far 

 as the upper end of the left ccelomic cavity. No pore canal opening exteriorly can be observed. 

 Part of the vestibulary wall is seen on the right side of the figure. The ciliated bands are 

 very distinct. 



PLATE V. 



(All figures of Tropiometra carinata. All X290.) 



FIGS. 1, 2, 3, 4, 5. From a series of longitudinal, frontal sections through an embryo 40 hours old. Figure 3 

 belongs to another series, but from a specimen of the same age and stage of development as 

 that of the other figures. The section has been turned the other way, so that the internal 

 cavities apparently show the inverse arrangement from the following figures. Figure 3 corre- 

 sponds to the section of the first series, which follows immediately after figure 2. The following 

 figure is separated from it by one section, and similarly there is one section between figures 

 4 and 5. Figure 1 gives a transverse section of the vestibulary invagination; the following 

 two sections go through the inner end of it, showing just a round mass of nuclei; there is still 

 a little trace of it in figure 4. Figure 2 shows the five primary processes from the hydroccel. 

 In figure 3 the hydroccel is seen to be still in the shape of a curve, not a closed ring, and it 

 is without connection with the parietal canal (p.c.). Figures 4 and 5 show the parietal canal 

 about to develop the pore canal (po. c.) which does not, however, reach through the ecto- 

 derm. The apical tuft of cilia is distinct in the section figure 5 and the two adjoining sec- 

 tions. In the ectoderm numerous glandular cells are seen. 



FIGS. 6-10. From a series of transverse sections through an embryo 40 hours old. There is one section 

 between figures 7 and 8, and likewise one section between figures 9 and 10, while two sec- 

 tions separate figure 8 from figure 9. Fig. 6 is from the anterior end, separated from figure 

 7 by six sections. 



PLATE VI. 



(All figures of Tropiometra carinata.) 

 Fias. 1-4. From a longitudinal, sagittal series of sections through an embryo 3 days old, nearly ready to 



attach itself. There are two sections between figures 1 and 2, and between 2 and 3, only 



one section between 3 and 4. The closure of the vestibulary invagination has begun. In 



figure 1 one of the primary tentacles is cut longitudinally. X290. 

 FIGS. 5, 6. From a series of transverse sections of an embryo 4 days old. Figure 5 is from the anterior 



end, with the vestibulary invagination, the chambered organ, and the parietal canal, the 



latter continuing only in one more section forwards. 

 Figure 6, which is separated from figure 5 by five sections, shows the pore canal (po. c.), which 



continues through two more sections downwards. It has no opening to the exterior. X290. 

 FIGS. 7, 8, 9. From a longitudinal section through an embryo 4 days old, pipe-shaped, with incompletely 



closed vestibulum. 





