408 UKOCHORDA [CH. XVIII 



from the hinder part of the body, which carries blood-vessels to it 

 and buds off cells into it which nourish it and change its character. 

 With these changes the adult form is attained. Few would see 

 any resemblance to a Vertebrate in the motionless sac-like body 

 fixed to a stone or rock and looking more like a plant than an 

 animal (Fig. 202). 



Nevertheless, the Tunicate in some points, even when adult, 

 recalls the structure of A mpUoxus. Thus we encounter 

 a<kat UCtUre a ring of delicate tentacles a short distance inside 

 the mouth strikingly recalling the velar tentacles of 

 AmpJiwxus. As in that animal also there is a long hypopharyn- 

 geal groove or endostyle passing in front into a peripharyn- 

 geal band, and secreting a cord of mucus which is worked forward. 

 This mucus is torn into strings by the inrushing current of water 

 and swept backwards to the opening of the oesophagus, entangling 

 in it food particles just as in AmpJiwxus. Instead of a hyper- 

 pharyngeal groove, there is a series of tags hanging down from 

 the dorsal wall of the pharynx, called languets. These in life 

 curve round so as to form a row of hooks supporting and directing 

 the mucous strings towards the oesophagus. 



The oesophagus leads into a dilated stomach which bends on 

 itself and leads into an intestine which after one or two coils runs 

 forward and opens into the atrial cavity. Its ventral wall is folded 

 inwards, forming a typhlosole similar to that of an Earthworm. As 

 usual the straight terminal portion of the intestine is called the 

 rectum. Near the anus open the ducts of the ovary and testis, 

 for the animals are hermaphrodite. These organs are branched 

 tufts of tubes, the testis being spread over the surface of the 

 stomach, the ovary forming a mass between the stomach and 

 intestine. Oviduct and vas deferens are closely applied to one 

 another, the vas deferens being the more superficial. The latter 

 opens by a rosette of small pores, the ovary by a broad opening, and 

 so the water from the gill-slits, as it passes out of the atrial cavity, 

 sweeps away the sexual cells. 



On the ventral side of the pharynx is a V-shaped heart, which 

 is enclosed in a space called the pericardium. The heart is only 

 a specially thickened part of a ventral blood-vessel, which lies im- 

 mediately under the endostyle and communicates through a network 

 of vessels in the gill trellis-work with the dorsal blood-vessel. 

 Waves of contraction pass over the heart so as to drive the blood 

 forward. After a certain interval the direction of these waves is 



