ANNELIDA OR ANNULATA 109 



The stomach-intestine has secretory cells that furnish a digestive 

 jfluid corresponding essentially to the pancreatic juice of the mam- 

 mals, as it digests proteins, carbohydrates and fats. Albumin is 

 broken down in y/2 hours at 37° C. in an alkaline medium, or 28>^ 

 hours in an acid medium. It is believed thac a peptolytic ferment 

 is present that accounts for slow digestion in an acid medium. An 

 amylotic ferment diastase changes starch into sugar (maltose). An 

 emulsifying ferment acts on the fats. Absorption is by osmosis and 

 the blood transports the nutriment. The rectU7n is the posterior 

 part of the intestine and has no typhlosole. It opens to the outside 

 through the posterior anus. 



Circulatory System. — There are 5 longitudinal blood vessels; 

 I dorsal, i ventral, i subneural and 2 lateral neural vessels; 5 pairs 

 of doj-sal hearts or aortic arches (7-1 1 somites). Parietal vessels 

 connect the dorsal longitudinal vessel to the subneural. 



In the first 12 somites the dorsal vessel is not a collecting vessel, 

 but behind the last pair of hearts in the nth somite, it receives 

 blood from the body wall and the alimentary tract. Two longi- 

 tudinal trunks lateral to the alimentary canal collect blood from the 

 anterior somites and passing posteriorly, join the dorsal vessel in 

 the 1 2th somite. 



From the posterior part of the body the blood is carried forward 

 in the dorsal vessel as far as the " hearts " which force it into the 

 ventral vessel. Valves in the aortic arches and dorsal blood vessel 

 prevent the blood from returning. The ventral vessel distributes the 

 blood, which flows anteriorly in front of the aortic arches and 

 posteriorly through the remainder of the body wall, nephridia, and 

 alimentary system. Aerated blood returns to the dorsal trunk 

 through the subneural and intestinal vessels. 



There are two distinct fluids which remain separated. The 

 coelomic fluid is found between the gut and the body wall. The 

 haemolymph is found in a series of closed tubes. The coelomic 

 fluid corresponds to the lymph of higher animals which bathes the 

 individual cells of the body. Haemolymph is apparently a solution 

 of haemoglobin. The red fluid corresponds to red blood corpuscles 

 of the blood of the higher animals and serves as a carrier of oxygen 

 to various cells and tissues of the body. 



In marine worms the respiratory pigment is called chloro- 

 cruorine. It is ^or^^jyr/w combined with iron. Some marine forms 

 like Arenicola and Nereis have brilliant red blood; Aphrodite and 



