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, mth) leads from the cavity of the oral 

 hood into the pharynx, and is surrounded by a mem- 

 brane, 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, Ir, and Fig. 109, A, /). 



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

 which are contractile, present certain undoubted homo- 

 logies with the more complex vessels of the Craniata, 

 and so a distinction is made between arteries and veins. 

 The arrangement of the chief of these may be seen from 

 the 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, nph] are 

 situated above the pharynx on either side in relation 

 with the reduced coelome in this region. The internal 

 end of each is provided with bunches of peculiar knob- 

 like cells projecting from closed nephrostomes : the 

 other end opens into the atrium (Fig. 109, A, }. 



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). There is no auditory organ. 



