Introduction to Annual Morphology. 233 



times with short tentacles ; it leads into a branchial 

 chamber often with plaited walls, whose lining mem- 

 brane is vascular (papillose in Chelyosoma), and shows 

 a deep, ventral, longitudinal, ciliated groove, bordered 

 by two mucous folds or lips. At the floor of this 

 ventral groove is an elongated, rigid, rod-like, whitish 

 organ, the endostyle, hollow, ciliated at its base, with 

 an outer sheathing layer of cylinder cells, within 

 which is a clear membranous layer, and two rigid 

 yellowish laminae. Betw r een the cutis and the mus- 

 cular layers are dorsal and ventral longitudinal 

 sinuses containing the blood, sending branches to the 

 branchial membrane. This branchial chamber varies 

 from a very small size to nearly the whole length of 

 the body (Pelonaia) ; it is homologous with the 

 breathing chamber of Balanoglossus ; it often exhibits 

 two ciliated bands extending from the front end of 

 the groove for the endostyle to beneath the ganglion. 

 The wall of the sac appears to consist of longitudinal 

 and transverse bands, crossing at right angles, leaving 

 quadrangular meshes ; these bands contain branches 

 from the dorsal and ventral sinuses. 



At the fundus of the branchial sac the oesophagus 

 opens, usually with radiating plicae, and no lip-like 

 ab-orally, often backwards, then di- 

 into a stomach, which may be fusiform, cvlin- 

 L, four-angled (Perophora), or with many inter- 

 nally projecting lamina' Dia/ona , or 'divided longi- 

 tudinally by seven <r rio-ht furrows stn -telling from 

 the cardiac t :i<l. It may ]><> simply 



striated, and tin- pylorus may be narrowed l>v a valve 



or by fleshy papill, Tin- outer wall of the sto- 



is striated in J Jrndp.doa, and the cavil;. Cellu- 



