CENTRAL COMPLEX. 



85 



line with the basement membrane of the ventral ectoderm of 

 the proboscis stalk. 



The central complex consists of the following parts : (1) 

 ventrally the notochord and, in the stalk, the skeletal develop- 

 ments of the basement membrane of the notochord (Fig. 64, n ; 

 Fig. 66, sk ; Fig. 60, 19), (2) the heart (Fig. 67, b, see also Figs. 

 60, 65), which is a blood vessel lying on the dorsal side of the 

 notochord, between it 

 and (3) the pericardium 

 (Fig. 64, per, Fig. 67, h, 

 see also Figs. 60, 65), 

 a closed sac of con- 

 siderable size and of 

 doubtful meaning, and 

 (4) the glomerulus or 

 proboscis gland which 

 is the well - developed 

 and folded coelomic 

 epithelium lying on 

 the front wall and 

 anterior part of the 

 sides of the pericar- 

 dium (Fig. 65, TO, Fig. 

 60, 2). 



The notochord has 

 already been described. 

 It extends along the 

 whole length of the cen- 

 tral complex and varies 

 very considerably 

 throughout the group. The basement membrane which lies 

 immediately outside its epithelium forms its sheath and is 

 especially thickened on the ventral side of the posterior part of 

 it (Fig. 64, n, Fig. 66, sk). This specially thickened part of the 

 notochordal sheath is continuous with a specially thickened 

 part of the basement membrane of the dorso-lateral buccal wall 

 (Fig. 64 en), and the whole constitutes the proboscis or nuchal 

 skeleton (Fig. 68). The proboscis skeleton consists of a median 

 body and of two limbs diverging backwards. The body is placed 

 ventral to the posterior part of the notochord in the neck of the 



FIG. 67. Transverse section through the hind end of the 

 proboscis, near the neck, of Glossobalanus minut us (after 

 Spengel). The section goes behind the glomerulus. 

 The epidermis is dotted and the nervous layer of the 

 epidermis is diagonally shaded, the basement mem- 

 brane of the epidermis is unshaded, adv blood vessels 

 of skin; b heart; div notochord; eh proboscis coelom 

 divided here into a right and left half by the anterior 

 end of ventral septum sv ; epv coelomic epithelium ; 

 h pericardium ; Im longitudinal muscles of proboscis 

 wall ; rev efferent vessels of proboscis ; rm circular 

 muscles ; sv ventral septum. 



