234 ARTHUR WILLEY. 



MM. Delage and Herouard retain the desi^jnalion nolo- 

 chord applied by Bateson to the diverticulum from the throat 

 which projects into the proboscis^ where it acquires a rigid 

 consistency and sustaining properties. I prefer to call this struc- 

 ture by a non-committal name, and propose the term stomo- 

 chord. The stomochord is not the only skeletal product of 

 the gut wall in the Enteropneusta. There is another structure 

 which finds no mention in the text-book under consideration, 

 but which is hardly second in interest to the stomochord itself. 

 It occurs along the entire length of the hind gut in the caudal 

 region on the ventral side in many Ptychoderidse ; it is a solid 

 keel-like, ribbon-shaped band, with dilated distal border abut- 

 ting upon the ventral blood-vessel, and united at its dorsal 

 edge with the median ventral epithelium of the gut. 



This structure, Avhich I propose to call the pygochord, 

 was first seen by Spengel in Pt. minuta, then by Hill in 

 Ft. hedleyi, and I have found it in Pt. flava, Pt. carnosa, 

 n. sp., and Pt. ruficollis, n. sp. 



In Spengelia alba, n. sp., it appears to be represented by 

 a vacuolar thickening of the ventral epithelium, which, how- 

 ever, retains its epithelial position, and is not draAvn out into a 

 band. 



I do not think that the enteropneustic stomochord corre- 

 sponds to any definite part of the true notochord. The prae- 

 oral extension of the notochord, far beyond the anterior limit 

 of the neural tube in Amphioxus, is due to a forward growth 

 of the notochord as such ; whereas the prjeoral position of the 

 stomochord in the Enteropneusta is due to a forward projection 

 of a portion of the collar-gut or throat. Spengel calls it the 

 Eicheldarm, but although he intended this name to be in- 

 different, it is capable of misleading interpretation, since it 

 does not belong to the proboscis at all in its primary quality of 

 integral constituent of the gut, but only in its secondary 

 quality of a skeletally metamorphosed derivative of the gut. 

 Moreover, whereas the notochord is essentially a uniform, 

 singlf, indivisible structure,^ the stomochord exhibits strongly 



' Tue auterior tip of the notochord presents certain properties which may 



