THE DEVELOPMENT OF AMPHIOXUS 43 



cavity on which they border must therefore to this extent be 

 lined with endoderm (Legros). 



3. The Club-shaped Gland 



The club-shaped gland lies far forward in the pharyngeal 

 region, and does not share in the shifting of the gill slits and 

 other derivatives of the pharynx with which it is at this time 

 connected only at a single point. During the early larval 

 period its dilated right end narrows and acquires an opening 

 into the pharynx (Fig. 14, A). This "gland" now is in the 

 form of a narrow tube, opening at the right end into the 

 pharynx and at the left to the outside. It is of doubtful 

 significance, both functional and morphological; it has been 

 compared with a gill slit and may represent the antimere of the 

 first primary, which is otherwise entirely lacking. It soon 

 atrophies like this gill slit and disappears without leaving any 

 trace (Figs. 14, 15). 



4. The Endostyle 



This appeared as a transverse, ciliated thickening, in the 

 floor of the pharynx in front of the club-shaped gland. As a 

 thickening of the pharyngeal wall the endostyle is involved 

 in the general torsion of this region and passes over to the 

 right side (Fig. 12). There its middle region draws back above 

 the primary gill slits, i.e., in the morphological mid-ventral 

 line, converting the transverse band into a > -shaped structure 

 with the apex directed posteriorly (Fig. 14). It continues to 

 extend backward, between the rows of primary and secondary 

 gill slits, while its limbs draw together coming into contact 

 and forming a double strip of cells, which in part become 

 differentiated as glandular cells. The endostyle is finally 

 carried back into a median ventral position by the time of the 

 critical stage (Fig. 15, B). 



From the anterior end of the endostyle two narrow ciliated 

 bands the rudiments of the peripharyngeal bands (Fig. 15, 



