CEPHALODISCUS. 



265 



laterally and ventrally it is produced into a free fold to 

 form the above-mentioned operculum. The collar-region 

 contains a section of the coelom which is precisely homolo- 



Fig. 127. — Longitudinal sagittal section through an adult Cephalodiscus. 

 CAfter Harmf.r.) 



The section is supposed to be taken sufficiently to one side of the middle line to 

 allow of the representation of one of the ovaries and one of the proboscis-pores. 



a. Anus. b.c. Trunk-coelom. c.c. Collar-ccelom. ch. Notochord. int. Intes- 

 tine, m. Mouth. W.J. .Nervous system. op. Postoral lamella (operculum). 

 ov. Ovary: the oviduct is deeply pigmented, p.c. Praeoral ccelom (cavity of 

 buccal shield). pk. Pharynx. /./. Proboscis-pore. ped. Base of pedicle. 

 St. Stomach. 



gous with the collar-cavities of Balanoglossus. As in the 

 latter form, it communicates with the exterior by a pair 

 of collar-pores which open at the level of the gill-slits. 



