248 



INVERTEBRATE MORPHOLOGY. 



vessels (h and /). One of these (/) divides (g) near the an- 

 terior extremity of the body, the two branches passing into a 

 circular vessel lying at the bases of the tentacles and sending 



branches up into them. The 

 vessels which return the 

 blood from the tentacles open 

 into a second ring external 

 to the first, and from it two 

 vessels pass backwards and 

 unite to form the second 

 longitudinal trunk from which 

 numerous csecal pouches 

 arise. All the vessels have 

 contractile walls, and the 

 blood which they contain 

 possesses nucleated red cor- 

 puscles. 



The digestive tract is bent 

 FIG. 112. LATERAL VIEW OF AN- upon itself (d and e), the 

 TERIOR REGION OF Phoronis (after mouth and anus, as already 



described, lying in close prox- 

 imity at the anterior extrem- 

 ity of the body. Several 

 regions, such as oesophagus, 

 first stomach, second stom- 

 ach, and intestine, are to be 

 distinguished, and along one 



BOURNE). 



a = lophophore. 



b = mouth, surrounded by epitome. 



c = lophopboral disk. 



d = O3sopliagus. 



f = intestine. 



/ = ventral blood-vessel. 



g = brancb of/. 



h = dorsal blood-vessel. 



i =- longitudinal muscle of body-wall, surface of the oesophagus and 



, intertentacular membrane. firgt s tomach runs in P. 



architecta a ridge, becoming a groove in the stomach region, 

 of ciliated gland-cells, which recalls the accessory intestine 

 of the Gephyrea. There are no special digestive glands. 



The nervous system is completely imbedded in the ecto- 

 derm. It consists of a nerve-ring, following the outline of 

 the lophophore at the bases of the tentacles and surround- 

 ing, therefore, the mouth but not the anus. From it a nerve 

 runs backward asymmetrically upou one side of the body 

 to near the posterior extremity. It contains a large clear 

 rod-like structure which seems to be a colossal nerve-fibre. 



