34 



Thyone which also eventually feeds on calcareous matter. The 

 aquarium in which the fresh Thyone's were put, frequently 

 contained an immense amount of small and very characteristic 

 calcareous bodies on the next day. I have not been able to 

 identify these, but according to some morphologists who were 

 especially acquainted with the local fauna, they ressemble very 

 much the calcareous sceletal elements of Alcyonarians. 



The same phenomenon, an acidity in the beginning of the 

 middle gut has also been observed by other authors in other forms. 

 Basch ') found it in the digestive tract of Blatta orientalis. 

 The secretion of the salivary glands, the contents of oesophagus 

 and fore-gut are acid. In the middle-gut („Chylusmagen") the 

 reaction is neutral in the first part, alcaline further on. Basch 

 explains it by an alcaline secretion of the crypts of the middle- 

 gut, Jousset de Bellesme assumes that an acid liquid, con- 

 taining pepsin, is poured into the beginning of the middle-gut by 

 the small coeca, found right behind the „Kaumagen". 



Biedermann 8) fed Tenebrio larvae on flour, added with 

 litmus. About two thirds (the first part) were colored red, the 

 rest blue. Similar results were obtained by Kovalevsky in 

 Muscidae, Blattidae and Tenebrionidae. 



These few references will serve to show, that an original 

 acidity, gradually passing over into alcalinity is by no means 

 rare in lower animals. The alcalinity in the very first part 

 of the gut of our Thyone is of course a complication due to 

 the fact that we have to do with a marine form here. The 

 sea water taken in with the food accounts for this alcalinity. 



In the next chapter we will report on our trials to find the 

 cause of the relative acidity in the present case. It does not 

 seem to be due to free acid in most cases; congo-red which 

 indicates free mineral acid, was never colored blue in B i e d e r- 

 mann's experiments — this might be due to the low Ph (4) 

 of the changing point (v. d. H.) — ; Giinzburg's reagent 

 (2 gr. phloroglucinol, 1 gr. vaniUin and 30 gr. absolute alcohol), 

 also indicating free mineral acid, especially hydrochloric acid, 

 gave the same result. It is not due to butyric or lactic acid 

 fermentation either, since lack of carbohydrates in the food 

 does not change the hydrogen-ion concentration. 



12. THE DIGESTIVE FLUID. 



Studies on the composition of the digestive juice in inverte- 

 brates are not so very abundant ; the only ones that have come 

 to my knowledge, are those of Biedermann (and Moritz) 

 on the intestinal contents of snails and of the larva of Tenebrio. 



The first question of importance is : „ What causes the relative 

 acidity of these juices?" Though not absolutely acid, they are 



') Sitzungsberichte Akad. Wien. 33. No. 25. 1859. p. 234. 



