748 



ZOOLOGY 



SECT. 



middle line ; and these, with the posterior folds, go to form the 

 completed funnel together with the " neck-muscles." For a time 



FIG. 660. Two later stages in the development of XiOligO, A, from the funnel side. B, obliquely 

 from above. Letters as in preceding figures ; ne. cart, nuchal cartilage (After Korschelt and 

 Heider.) 



B 



FIG. 661. Two stages in the development of IiOligO. later than those represented in Fig. GOO. 

 From the anal or funnel side. Letters as in preceding figure ; in addition, ftn, fins. (After 

 Korschelt and Heider.) 



the edges of the two folds which form the funnel remain free ; 

 eventually they coalesce to form a complete tube. 



