LANCELETS 305 



by an unsegmented supporting rod, or notochord (K). Neither a skull nor 

 a heart is developed. The blood, which is colourless, is driven through the 

 body by the larger bloodvessels. There are neither organs of hearing nor 

 eyes, such, at least, as (with few exceptions) we find in all other verte- 

 brates. Light sensations are, however, transmitted by minute organs 

 furnished with cups of black pigment, which are situated in the spinal 

 cord (EM). The olfactory organ is a minute pit. The mouth (M) consists 

 of a longitudinal slit surrounded by numerous ciliated filaments, or cirri. 

 The water entering the mouth passes into the branchial sac (KS), which 

 is perforated by numerous clefts. Through these the water flows into 

 the space (RK) which surrounds the branchial sac, and is discharged 

 from the body by the opening (0). The food taken in with the water, 

 and consisting of microscopic animals, passes into the intestine (D), 

 which terminates in the anus (A). 



