716 A. T. MASTER MAN. 



clujrJ '^ of Haniier, with its homology to the simihifly iiainecl 

 structure in Balanogl oss us. Lastly, the terms pericardial 

 sac, glomerulus, and ectodermal pit are adoj)ted for organs 

 in Cephalodiscus which seem to be homologous with simi- 

 lai'ly named organs in Balanoglossus. 



In the region lying between the buccal shield and the 

 collar of Cephalodiscus are several important organs, the 

 exact relationships of which have not previously been fully 

 determined. This area may be described as the central com- 

 ])lex, a convenient term already applied to the same region in 

 Balanoglossus. In this region there are externally the 

 ectodermal pit, the pre-oral pores, and the central nerve-mass ; 

 interually are the subneural gland, certain important blood- 

 vessels, the pericardial sac, and the meseiitei'ic walls of the 

 pre-oral and collar cavities, together with the glomerulus and 

 muscular strands. The general outlines of the subneural 

 gland and the pre-oral and collar cavities have been indicated 

 by previous workers (Mclntoshs, Harmers) and by myself, 

 but a detailed examination by carefully orientated and serial 

 sections has brought to light some interesting new facts. 



We may describe the organs under the following headings : 



1. Ectoderm and nervous system, ectodermal pit, pre-oral 

 pores. 



2. Subneural gland and pharynx. 



3. Pericardial sac, pro-oral cavity, ]ire-oral canals, glome- 

 rulus, collar cavities, and blood-vascular system. 



1. Ectoderm. — Figs. 1 — 8 all illustrate the condition of 

 the ectoderm in this region. Ventrally the ectoderm on the 

 buccal shield consists of long narrow epithelial cells with 

 numerous unicellular glands, which form a buccal gland as 

 described by Mcintosh (6). Tliis e])ithelium is not shown 

 here. Dorsally it consists of columnar ejiithelial cells with 

 a very definite cuticle. lu the region of the central nervc- 

 nuiss the inner ends of the cells are seen to ])ass downwards 

 as delicate fibres, terminating in jx'culiar conical ganglion- 

 cells (figs. 1 and 2). At their base these ganglion-cells give 

 off otlier delicate fibres ruunin<>' forwards and backwards. 



