SPENGELIA, A NEW GRNUS OP ENTEROPNEUSTA. 627 



posterior gill-slits, the dermal pits do not comrnunicate with 

 the intestine; although they extend very near to the wall of 

 the latter. 



Internal Structure. 



1. Vermiform Process of Notochord. — This is a long, 

 generally solid cord of cells, lying in the centre of the pro- 

 boscis, and surrounded by a stout limiting membrane, which 

 serves for the insertion of the median dorso-ventral muscles 

 of the proboscis. Its diameter is not quite equal throughout 

 its course. It agrees closely with the corresponding process 

 in Glaudiceps, particularly in the fact that the ventral 

 septum of the proboscis does not accompany it, as it does in 

 Schizocardium. r — 



2. Collar Nerve-cord.— One of the most interesting and 

 generically important characters of Spengelia is the occurrence 

 of vestigial dorsal roots. They do not reach the epidermis, 

 nor do they contain fibres or "Punktsubstanz." Otherwise 

 their similarity to the roots of Ptychodera is complete. I have 

 seen two such roots in Spengelia. The anterior root is the 

 longer, and it runs obliquely, so that it appears in several 

 sections separate from the nerve-cord. It is mostly solid, but 

 contains a few minute disconnected cavities. The posterior 

 root is hollow and much shorter than the anterior root, so that 

 it does not appear in section separate from the nerve-cord. 



3. Splanchnic Nerve -fibres. — A rather puzzling feature 

 in the anatomy of Spengelia is the occurrence of a layer of 

 nerve-fibres (Punktsubstanz) at the base of the epithelium of 

 the buccal or throat cavity. Anteriorly it is a thick layer, and 

 it becomes gradually thinner posteriorly. It may be traced as 

 a very thin layer for a long distance beyond the opening of 

 the notochord into the buccal cavity, and even at the base of 

 the epithelium forming the oesophageal portion of the branchial 

 sac. The occurrence of this well-defined layer of splanchnic 

 nerve-fibres round the throat and oesophagus alone distin- 

 guishes Spengelia from all other Euteropueusta. 



