NiCKERSON, Epidermal Orga7is of PJiascolosoma. 221 

 Summary. 



1. The complex nervous system produced in the budding 

 process arises either (i) from the cells of the nerve cord, or 

 (2, and chiefly) from ectodermic ingrowths. 



2. There are five regions in the ectoderm which may give 

 rise to nervous elements: (i) a single median ventral region 

 (i, Fig. i) especially active in producing the median portion of 

 the cord in the new segments of the anterior zooid ; (2) a re- 

 gion, on either side, superficial to the latero-dorsal muscle band 

 (3, Fig. i), which produces the brain in the posterior zooid ; 

 and (3) a region on each side, superficial to the latero-ventral 

 muscle band (2, Fig. i), concerned in the development of the 

 sub-pharyngeal ganglia. 



3. The brain arises in the region immediately contiguous 

 to the lateral line cells ; and the ectodermic ingrowths marking 

 the point where the connective re-enters the body cavity from 

 its position superficial to the muscle band appear in connection 

 with these cells. If the cells of the lateral line are nervous, they 

 are thus brought into relation, in an interesting way, with the 

 central nervous system. The brain, in this event, is developed 

 in connection with the lateral line cells, while the ventral cord 

 is derived from elements much more ventral. 



Epidermal Organs of Phascolosoma gouldii. 



By Margaret L. Nickerson. 



Scattered abundantly over the introvert and body of this 

 worm are found the epidermal organs which on the introvert 

 have the form of papillse, while on the trunk they are partially 

 included in the large excavations on the inner surface of the 

 cuticula. These bodies are ovoidal in shape with the smaller 

 end directed outward, while the large base rests upon the circu- 

 lar muscle. Each is surrounded by a delicate membrane which 

 is probably an invagination of the membrana propria. 



