324 ENTEROPXEUSTA FROM THE SOUTH PACIFIC, 



The change of function which would be associated with the transformation of the 

 relatively undifferentiated parabranchial ridges into such a highly specialised organ as 

 the endostyle is not easy to define 1 , and I limit myself to pointing out the similarity 

 in topographical relations. 



Vend 



Fig. 7. Diagrams to illustrate the comparison of the specialised ciliated tracts in the pharynx of 



amphioxrs i a) axd esteropneusta (b). 

 end Endostyle. plib Peripharyngeal bands, pb Parabranchial ridges, epb Epibranchial band. 



It is satisfactory to know that there exists something in the Enteropneusta which 

 may be related to the endostyle but which nevertheless is not one. 



The phyletic series of changes relating to the endostyle may therefore be tabu- 

 lated as follows : — 



I. II. III. 



Parabranchial ridges Endostyle Thyroid 



(Enteropneusta) (Cephalochorda and Urochorda) (Vertebrata) 



1 Of course it would be connected with changes in the entire habit of life, method of feeding, and quality 

 of food. 



Zoological Laboratory, 

 New Museums, Cambridge, 

 May 1st, 1899. 



