424 THE LANCELET CHAP. 



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

 the endostyle (Fig. 109 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. 107, mtti) leads from the 

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

 by a membrane, the velum (vl}, produced at its edge into 

 a number of tentacles (vl. t). 



The intestine is straight (Fig. 107, int) and the hepatic 

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

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

 pharynx (Fig. 107, /rand Fig. 109 A, /). 



Although no heart is present, the blood-vessels, some of 

 which are contractile, present certain undoubted homologies 

 with the more complex vessels of the Craniata, and so a 

 distinction is made between arteries, and veins. Their 

 arrangement may be seen from the accompanying diagram 

 (Fig. no), which should be compared with Fig. 83 and 

 later on with Fig. 119. Blood occurs in certain spaces 

 as well as in the vessels. 



The numerous nephridial tubes (Fig. 107, npJi) are situated 

 above the pharynx on either side in relation with the 

 reduced ccelome in this region. The internal end of each 

 is provided with bunches of peculiar knob-like cells pro- 

 jecting from closed nephrostomes : the other end opens into 

 the atrium (Fig. 109 A, n). 



The spinal cord has a dorsal fissure but no ventral fissure 

 (p. 155). Its central canal widens out in front (Fig. 107, 

 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 end is a 

 ciliated depression usually known as the olfactory pit (olf. p). 



