GLOMERULUS. COLLAR COELOM. 87 



portion of its cavity (e.g. Glossobalanus ruficollis, etc.). Its 

 ventral wall is concave, slightly enveloping the dorsal sides of the 

 notochord, and contains a number of transverse muscular fibres 

 which being in contact with the heart tube very likely cause the 

 pulsations by means of which the blood fluid is moved. In 

 Schizocardium (hence the name) and in Glandiceps the anterior 

 lateral portions of the pericardium are produced into two tubes 

 which extend along the vermiform process of the notochord and 

 constitute the auricles of the pericardium. In Bal. carnosus the 

 pericardium is bifid anteriorly, being produced into two pouches, 

 accompanied by glomerulus tissue, beyond the anterior limit 

 of the notochord. 



As already stated the dorsal wall of the posterior part of the 

 pericardium is in contact with the basement membrane of the 

 ectoderm, thus giving rise to the dorsal septum ; but its anterior 

 wall and the anterior part of its dorsal wall, and its side walls 

 are covered by coelomic epithelium which is much folded and 

 composed of large cells containing pigment grains. This is the 

 glomerulus. Within the folds, i.e. between their epithelium and 

 the pericardial wall are some blood vessels which are in direct 

 communication with the heart. If the glomerulus is an excre- 

 tory organ, as is supposed by some, its secretion must pass into 

 the proboscis coelom, reaching the exterior by the proboscis pore. 



The collar coelom is in many species almost entirely filled up 

 by the muscular and connective-tissue development of its walls, 

 and, except in the parts of it known as the collar canals, is 

 devoid of a lining epithelium. The two lateral sacs of which it 

 originally consists meet dorsally above the collar nerve-cord and 

 ventrally below the gut (Fig. 69). The longitudinal mesenteries 

 formed by the opposed walls of these sacs persist only in part : 

 the ventral mesentery is present in the posterior region for a short 

 distance, but is deficient over the greater part of the collar ; the 

 dorsal mesentery which extends between the nerve cord and the 

 skin persists over the greater part of its length, but is deficient 

 anteriorly. In Harrimania kupfferi both mesenteries are absent 

 in the adult, and it is quite possible that there may be consider- 

 able variation in them in other species. 



In some genera (Ptychodera, Schizocardium, Spengelia and 

 Dolichoglossus), the coelomic sacs of the collar are in parts 

 separated from the gut wall by the peripharyngeal cavities (Fig. 69) 



