PHYSIOLOGY OF THE INVERTEBRATA. 85 



other genera besides Uraster, the pyloric casca or diverticula 

 of the Astcridca are proved to be pancreatic in function. 



Dr. L. Fredericq (the distinguished Professor of Physiology 

 in the University of Liege) has obtained similar results, but 

 by an entirely different method. Fredericq obtains various 

 aqueous extracts (neutral, alkaline, and acid) of the cteca 

 previously hardened in alcohol. These extracts each contain 

 the digestive ferments. They digest cooked and raw fibrin 

 exceedingly well in alkaline extracts. This action is less 

 active in neutral extracts, and is almost nil in acid extracts. 



The pyloric caeca of the Astcridea are consequently diges- 

 tive organs — their function being similar to that of the pan- 

 creas of the Vcrtchrata. 



Dr. MacMunn* has shown that these pyloric casca " con- 

 tain a large quantity of enterochlorophyll, mostly dissolved 

 in oil, which may possibly act in supplying oxygen to the 

 tissues of the animal, perhaps from the waste carbon di- 

 oxide." If this be correct, the pyloric cteca perform a dual 

 function — that of a digestive and a respiratory organ. 



It may be stated that the stomach or pyloric sac of 

 Uraster ruhcns is a digestive cavity and a renal organf — i.e., 

 it has a dual function. Darwin states, in The Orirjin of Speeies 

 (chap, vi.), that " numerous cases could be given among the 

 lower animals of the same organ performing at the same time 

 wholly distinct functions ; thus, in the larva of the dragon- 

 fly and in the fish — Cohites — the alimentary canal respires, 

 digests, and excretes." 



The Trichoscolices. 



Dr. Fredericq has investigated the nature of digestion in 

 Tccnia scrrata (one of the Cestoiclea), which inhabits the 

 small intestine of the dog. His experiments were conducted 

 in the following manner : — Three tape-worms, killed by chloro- 



* Froc. Birm'uKjhum Philosop. Soc. vol. 5, pt. i. p. 214. 

 t See Dr. A. B. Griffiths' paper in Proceedings of lioyal Society of London, 

 vol. 44, p. 326. 



