PLATE XXV 



ONTOGENY OF THE LOOP IN TEREBKATALIA OBSOLETA 

 Ball (Pages 408, 409) 



Figure 1. — Interior of dorsal valve in early cistelli/orm stage; show- 

 ing median septum and dental sockets. X 25. 



Figure 2. — Side view of septum of preceding. X 26. 



Figure 3. — A little later stage ; showing gTowth of two transverse 

 expansions on septum. X 25- 



Figure 4. — Side view of same. X 25. 



Figure 5. — Beginning oi platidiform stage ; showing groove on edge 

 of septum, with arched covering at posterior end, and growth of crural 

 processes. X 25. 



Figure 6. — Side view of same. X 25. 



Figure 7. — Side view of septum at a later stage, just before growth 

 of descending branches of loop ; showing form and position of ascending 

 branches, or secondary loop, and septal characters. X 25. 



Figure 8. — Platidiform stage ; showing union of descending branches 

 with septum. X 12. 



Figure 9. — Beginning of ismeniform stage; showing growth of as- 

 cending branches. X 12. 



Figure 10. — Early muhlfeldliform stage; showing holes developed in 

 ascending branches by resorption. X 12. 



Figure 11. — Oblique view of septum, with ascending branches 

 broken off. x 12. 



Figure 12. — Beginning of terebrataliform stage ; showing union of 

 ascending with descending branches. X 12. 



Figure lo. — A little later stage; showing resorption of broad de- 

 scending branches. X 7. 



Figure 14. — Late adolescent stage ; showing connecting bands from 

 descending lamellce to septum, x 2-|. 



Figure 15. — Fully adult loop, with connecting bands. X 2^. 



