76 



PHYSIOLOGY OF THE INVERTEBRATA. 



From the stomach passes the intestine, which terminates in 

 an anal aperture situated at the posterior end of the body. 

 The mouth is provided with a proboscis. 



(2) The Urodiordata or Tunicata. — As an example of this 

 order we describe Fhallusia mcntula (Fig. 22). The oral 



aperture leads into the 

 pharyngeal - respiratory 

 chamber, from which 

 the oesophagus, situated 

 on the posterio-neural 

 side of the body, selects 

 the food particles intro- 

 duced into thatchamber 

 by the action of small 

 tentacula. The walls 

 of the pharyngeal-re- 

 spiratory chamber are 

 gathered into ciliated 

 folds, which have a 

 number of slit-like per- 

 forations. These act 

 as a kind of sieve. On 

 the ha3mal side of the 

 pharynx there is a 

 ciliated groove bounded 

 by two glandular folds 

 (the endostyle). The 

 oesophagus leads into 

 an internal-folded sto- 

 mach. The intestine, 

 which forms a loop, terminates in an anus situated opposite 

 the atrial or cloacal aperture on the neural side of the body. 

 The Savigny tubules lie upon, and open by a duct into, the 

 stomach. These tubules also ramify over the wall of the 

 intestine, and are pancreatic in function. They are present 

 in nearly all the Tunicata* 



* See Chandelon in Bull. Acad. Be'g., 1875 ; and Dr. W. A. Herdman in 



Fig. 22. — Alimentary Canal of 

 Fhallusia. 



a = moutl). b = tentacles. c — intestine. 

 d = stomach, c = heart. / = oesophagus. 

 g = Savigny's tubules, k = anus, k = atrial 

 aperture. 



