PHYSIOLOGY OF THE INVERTEBRATA. 51 



a stomach, the posterior end of which gradually lessens in 

 diameter and finally passes into the intestine. The stomach 

 is lined internally with a dense rugged membrane. " The 

 distinction between the stomach and intestine is effected, as 

 Van der Hoeven has shown, by a conical valvular pylorus, 

 which projects into the commencement of the intestine. 

 The hepatic mass, composed of contorted slender caeca, 

 which with the generative glands fills the greater part of the 

 cephalo-thoracic cavity and also extends into the abdomen, 

 pours its secretion into the commencement of the intestine 

 by two ducts on each side." 



The so-called liver or hepatic mass is a very large organ in 

 the Crustacea ; but its secretion answers chemically to that 

 of a pancreas — in fact, this organ is nothing more than a 

 pancreas or digestive gland. In Limulus there is a short 

 rectum opening into a kind of cloaca. 



(21) The Trildbita form an extinct order of Crustacm. 



(22) The Phyllopoda. — In this order the alimentary canal, 

 as represented by Apus, is very simple. The mouth is 

 situated anteriorly on the ventral side of the body, and leads 

 into a vertical oesophagus which finally bends back into a 

 small stomach. The stomach passes into a straight intestine, 

 the latter terminating in an anus situated below the terminal 

 segment. The pancreas (the so-called liver) is situated in 

 the head, and consists of many csecal tubules branching from 

 the stomach. There are two salivary glands whose secretion 

 is poured directly into the stomach, these glands beiqg 

 situated above that organ. 



Dr. G. 0. Sars (the distinguished Professor of Natural 

 History in the University of Christiania) has very fully 

 described the digestive system of Cydestheria hislopi* a new 

 generic type of bivalve Phyllopoda. 



In Cydestheria hislopi the mouth, "located between the 

 masticatory parts of the mandibles, is generally covered 



* See Christiania Videnslcabs — Selskabs Furliandlirujer, 1887, No. i, pp. 28 

 audi 40. 



