4o8 THE LANCELET chap. 



intervening bars are seen to be arranged in couples, the 

 supporting rods {br. r. i) of the primary bars (br. sep. i) 

 being forked below. A further complication is produced 

 by the formation of transverse connections, supported by 

 skeletal rods, between the gill-bars. The gill-slits are more 

 numerous than the muscle-segments or myomeres (tnyom), 

 and owing to their obliquity, a large number of them always 

 appear in a transverse section (Fig. loo, A). 



On the ventral wall of the pharynx is a longitudinal groove, 

 the endostyk (Fig. loo A, e), lined by ciliated and glandular 

 cells; and a somewhat similar groove, the epipharyngeal groove, 

 extends along the dorsal aspect of the pharynx : these serve 

 as channels along which the particles of food pass into the 

 intestine. The minute mouth (Fig. 99, mtK) leads from the 

 cavity of the oral hood into the pharynx, and is surrounded 

 by a membrane, the velum (&/), produced at its edge into 

 a number of tentacles (vl. t). 



The intestine is straight (Fig. 99, int) and the hepatic 

 CKCum, or rudimentary liver, arises from its anterior end on 

 the ventral side, and extends forwards to the right of the 

 pharynx (Fig. 99, Ir and Fig. 100, /). 



Although no heart is present, the blood-vessels present 

 some similarities to those of the Craniata. Their arrangement 

 may be seen from the accompanying diagram (Fig. loi), 

 which should be compared later on with Fig. no. The 

 nephridial tubes (Fig. 99 nph) are situated above the pharynx 

 on either side and open on the one hand into the reduced 

 ccelome in this region, and on the other into the atrium 

 (Fig. TOO, n). 



The central canal of the spinal cord widens out in front 

 (Fig. 99, br) to form a small cerebral ventricle {en. coe) in 

 the front wall of which is an unpaired pigment spot, 

 representing a simple kind_of eye (e. sp), and at its anterior 



