1891.] Processes of Ammocoetes. 255 



The only glandular organ in connection with the intestine is 

 the liver, with its large gall-bladder ; in structure it is typically a 

 tubular liver throughout, and there is no evidence of any differen- 

 tiation of function in the cells. 



Round the entrance of the bile-duct into the intestine are a 

 few small glandular follicles which have received the name of 

 pancreas, but in most specimens they are too few and too small for 

 it to be possible that they could play any important part in diges- 

 tion, at all events during the Ammoccetes-stage. After transfor- 

 mation the liver becomes completely separated from the alimentary 

 canal, the duct becomes obliterated, and the liver itself undergoes 

 fatty degeneration. At the same time the small glands in the 

 wall of the intestine which have been called the pancreas increase 

 in number and form quite a prominent ring. If these glands are 

 pancreatic in function, it suggests itself that possibly the tryptic 

 digestion may become more important than the peptic as the 

 animal advances to the higher stage of evolution in the adult 

 Petromyzon. I hope to be able to work out the digestive processes 

 of the adult animal as soon as I can obtain material. 



Finding the presence of a peptic ferment to be so general in all 

 parts of the alimentary canal, the question arises if it is present 

 also in other tissues of the animal. I have already mentioned that 

 no sign of digestive activity can be obtained from extracts of the 

 so-called thyroid, extracts of the central nervous system are also 

 quite inactive, and extracts of muscle shew only the faintest signs 

 of activity after many hours. Then I thought it might be of 

 interest to test for peptic ferment in the skin as being an epithelial 

 structure continuous with the lining of the pharynx and on account 

 of its active secretion ; and I found that a "2 °/ HC1. extract of 

 the skins of two Ammocoetes digested 1 c.c. fibrin in a little over 

 1 hr. The skin consists of several layers of cells, the most super- 

 ficial being those which secrete. They are peculiar in having a 

 very thick cuticular border, whose striated appearance is due to 

 the presence of fine pores through which the secretion exudes. 

 These cells are full of granules and when treated with methylene- 

 blue in the living condition, as observed by Mr Hardy, the granules 

 at the base of the cell stain blue, whilst those towards the surface 

 appear rose-coloured in artificial light ; this reaction he has every 

 reason to believe indicates the presence of a zymogen. 



As to the significance of this secretion, it does not seem 

 probable that it could function in the digestion of food. I think 

 it must have some important function, and considering the habits 

 of the animal, which lies buried in the mud, Mr Hardy has sug- 

 gested that this secretion of the skin may act as a protection 

 against the attacks of bacteria and other organisms, which might 

 otherwise be injurious. 



