Plate V. 



All the figures represent sections along the sagittal plane of a grown specimen of Tjalfiella 

 tristoiiia. in consecutive order from tlie tentacle to the apical organ; all equally enlarged: 22/j. 



Fig. I. Section through the tentacle-base, outside the genital organs. 



— 2 — 5. Sections through the outer (subtentacular) genital organs and the tentacle basis. 



— 6 — 8. The subsagittal (inner) genital organs appear below the outer ones (this position being 



partly due to the contraction of the .specimen). The tentacle basis gradually disappears in 

 these sections. Contemporaneous!)- the invagination over the genital organs appears. In 

 Fig. 6 the cavity of the two sides of the tentacle basis is seen to be in connection with 

 the gastrovascular canals. In fig. 7 the same is seen to be the case with the cavities of 

 the two outer genital organs. 



— 9. Inside the tentacle basis. The two canals are seen to lie separately. 



— 10. • The two canals unite into one (the transverse canal). The outer genital organs have dis- 



appeared. 



— II — 12. Showing the connection of the cavity of the two inner (subsagittal) genital organs with the 



transverse canal. Further the ectodermal invagination over these genital organs is seen 

 here (as also in fig. 13). 



— 13. The testicular portion of the subsagittal genital organs has disappeared, only the ovarial 



portion remaining. 



— 14—16. The excretory canals are shown. — Fig. 16 especially shows them, being almost exactly 



a median section. (Comp. PI. VII. Fig. i). 



In figs. 10—16 is seen a brood cavity on each side near the basis. The content has not 

 been drawn, being not sufficiently well jjreserved and the sections not having such a 

 direction as to show anything of the embryonal structure clearl)-. 



A detailed explanation of the figures otherwise seems unnecessary. An inspection of 

 the figures in their consecutive order will show the interrelations of the different organs 

 clearly enough. 



