RECENT WORK ON THE PROTOCHORDA. 



235 



marked regional difFeienliatioii (Fig. 3). It is tlieiefore not 

 sufficient to say that any stvuclure in other forms is compar- 

 able to the enteropneustic stomochord, but it must be specified 

 which portion of this structure is referred to. 



Fig. 3. — ^Diagram of a complete stomochord of au Euteropueust from tLe 

 dorsal and lateral aspects, to show its regional diti'erentiation. v.)). 

 Vermiform process, a.s. Anterior region of body of stomochord. l.p. 

 Lateral pouch, v.c. Ventral csecum. n. Nuchal region, b.o. Buccal 

 orifice of stomochord. e.g. Throat or collar-gut. 



The lumen of the stomochord is highly variable ; it may 

 safely be said that it is not the same in any two individuals of 

 a species. Sometimes it is in a fragmentary condition, some- 



have an atavistic significance, but this does not affect my general proposition. 

 The most that could be looked for in the embryos of higher Chordata would 

 be a vestige of the buccal orifice of the stomochord, and perhaps this does 

 occur. 



