90 AnneliJes, 



villi in the intestine, in its undistended state, nearly fill up the whole 

 calibre ; they are arranged in longitudinal rows, and when examined 

 in a leech newly killed, with their epithelial investment entire, they 

 form a beautiful subject for microscopical investigation. 



Food. — If the alimentary canal of the horse-leech (fig. /, p. 17) be 

 now compared with that of the medicinal species (fig. m), one cannot 

 fail to observe many striking difierences between the two ; the sto- 

 mach in the one being nearly a simple cylindrical tube, whilst in the 

 other it is provided with large lateral sacs or pouches. The cceca, 

 which, in the horse-leech, are so small as to be very easily overlooked, 

 are in the medicinal one of so large a size as to occupy nearly the in- 

 ferior fourth of the body ; the intestine, too, which in the former ani- 

 mal is equal in diameter to the stomach itself, in the latter is so small 

 as to have led many anatomists to deny its existence. These facts, 

 combined with others which have been already alluded to when de- 

 scribing the very great differences in their dental apparatus, cannot 

 fail to prove that the two species must differ as widely in their habits 

 and the quality of their food. It is still maintained by some authors, 

 and the name — horse-leech — which has been given to this species, 

 would tend to support the opinion, that it lived by sanguisuction, and 

 poisonous effects have been attributed to its bite ; but many persons, 

 whose veracity cannot be doubted, after repeated trials have failed to 

 make this species adhere to the human skin. Any one who will keep 

 a few horse-leeches in a bottle, and supply them with worms or the 

 larvae of insects, wull soon be convinced of the voracity of their appe- 

 tite, for they will devour the medicinal leech, and even individuals of 

 their own species. All this is perfectly intelligible, and what an ex- 

 amination of the arrangement of their digestive apparatus, would lead 

 us to suspect was the nature of their food. The medicinal leech, on 

 the contrary, provided as it is with upwards of two hundred cutting 

 teeth, and with a capacious sacculated stomach, with a small oeso- 

 phagus and still smaller intestine, is eminently qualified for subsisting 

 on liquid food ; and as it is a well ascertained fact, that when once 

 they have gorged themselves, the blood will remain for a very long 

 time in their stomach, to all appearance in an unaltered state, it would 

 follow either that their digestive powers must be exceedingly slow, or 

 that the food which they take in with such avidity cannot afford them 

 much nourishment. Is it not more probable, as Professor Rymer 

 Jones has suggested,* that the complicated stomach and inferior den- 



* ' General Outline of the Auinial Kingdom,' p. 103. 



