58 PHYSIOLOGY OF THE INVERTEBRATA.. 



into which numerous pairs of pancreatic follicles discharge 

 the digestive fluid. The intestine becomes narrower at the 

 posterior end, and terminates in an anus situated behind the. 

 twentieth somite. 



(31) The Anovioura form a small order containing the 

 hermit-crabs {Paguridce). They are distinguished from' the 

 Macroura in having an uncalcified and soft integument. The 

 appendages of the body are more or less abortive through disuse, 

 while those of the sixth somite are modified to form claspers. 

 By means of the claspers the hermit-crabs are capable of 

 holding on to the columellse of the shells of Molluscs which the 

 Paguridce inhabit. The inner part of the Aiwmoura are 

 somewhat similar in structure to those of the Mcicroiora. 



(32) The Brachyura. — This order includes the crabs. The 



abdomen is small and without a caudal " fin." It is curved 



round against the channelled ventral surface of the thorax. 



The mouth lies between the mandibles, and is a wide aperture, 



bounded by the labrum in front and the metastoma behind. 



It leads into a wide but short oesophagus. The oesophagus 



opens almost ventrically into a large stomach of globular 



form. The walls of the stomach, as well as those of the 



oesophagus, are lined by a chitinous extension of the exo- 



skeleton — the so-called teeth. The function of these chitinous 



teeth is to divide and macerate the food before it passes into 



the intestine. The posterior part of the stomach of the 



Brachyura gradually lessens in diameter, and then leads into 



the intestine. " The intestine passes backwards with a slight 



vertical bend to the base of the penultimate abdominal 



segment." The so-called liver, which is essentially pancreatic 



in function,* consists of two symmetrical halves. This large 



bilobed organ extends the whole length of the cephalo-thorax ; 



and the numerous csecal tubes (arranged in tufts), of which it is 



composed, are clearly seen under the surface of water. The 



CBecal tubes of each half of the digestive organ lead into a 



* Dr. Griffiths' paper in the Proceedings of Boyal Society of Edinhmglt, 

 vol. 16, page 178. 



