THE (ESOPHAGUS, STOMACHS AND INTESTINES. 417 



these Malpighian tubules, and I see no objection to ascribing 

 an hepatic function to them. 



That the Malpighian tubes are the morphological representa- 

 tives of the vertebrate liver is no contention of mine. If the 

 ' so-called ' livers of crabs, molluscs and other invertebrates are 

 in future to be spoken of as pancreates, I suppose the Mal- 

 pighian tubes should be so named. Fashions change, but it is 

 difficult for one who has spoken of a gland for forty years as a 

 liver, to see the impropriety of the term because some recent 

 writers have suddenly discovered that it should be called a 

 pancreas. 



That something may be said in favour of the term liver or 

 hepato-pancreas does not seem doubtful to me ; I know no 

 vertebrate in which the cells of the pancreas are loaded with 

 pigment and oil-drops, like those of the so-called livers of many 

 invertebrates. 



I do not wish to discuss this matter further, as it is only a 

 question of convenience. One term is as good as the other if 

 the meaning is obvious, and I cannot conceive how, with this 

 explanation, any difficulty can occur in understanding anything 

 I have written on the subject. 



c. The Rectal Papillae. 



The Rectal Papillae are four hollow, conical bodies, two on 

 each side, which project into the rectum. They are about 

 75 mm. in length, and from '25 mm. to '3 mm. in diameter at 

 their base. 



The wall of the papilla is composed of a single layer of large 

 pyramidal cells, which are from 40 p to 80 p, or even 'i mm. in 

 length : their rectal surface is covered by a cuticular sheath, 

 the outer sheath, continuous with the lining cuticle of the rectal 

 pouch ; the inner extremities of the cells rest on a reticular 

 connective pouch, the inner sheath, which bounds the cavity of 

 the papilla (Fig. 52). 



The base of the papilla is covered by a layer of radiating 

 muscle-fibres, which connect the inner and outer sheath. 



The cavity of the papilla is continuous with the body cavity ; 



282 



