1893.] and Functions of the Alimentary Canal o/Daphnia. 49 



apart than usual and often do not reach the surface of the 

 border. 



In any one section the granules of different cells are rather 

 differently preserved. Some of the cells appear lighter than the 

 rest, and these are generally broader ; possibly in them swelling 

 of the granules has begun, while in the others the granules are 

 better preserved. 



In sections through fasting animals which have been pre- 

 served in absolute alcohol the epithelium shows large clear (i.e. 

 unstained) spaces alternating with narrow threads or columns of 

 staining substance. The spherical nucleus may sometimes be 

 seen attached as it were to one side of the staining column and 

 projecting into the clear space. In many cases the clear space 

 contains scattered granules which have not swollen up. 



The discharge of the granules into the lumen of the gut 

 may not unfrequently be seen in osmic vapour preparations 

 especially of fasting animals. They appear in places to be 

 streaming from the cells through the border and to form a 

 homogeneous mass in the lumen which sometimes imbeds still 

 unaltered granules. 



These granule-bearing or gland cells occur throughout the 

 length of the gut, but they are most numerous in the middle 

 or digestive region. They are fewest in the short neck-like 

 region, already alluded to, which is just posterior to the junction 

 of oesophagus and mesenteron. 



It is interesting to note that quite at the posterior end of 

 the mesenteron gland cells occur which contain remarkably com- 

 pact groups of granules which stain deeply with osmic vapour. 

 These like the other granules are best seen in starving animals. 



We may correlate the existence of these cells in this particular 

 position with the formation of the fseces which takes place in this 

 region. The faeces are composed of the innutritious detritus of 

 the food stuffs glued together by some substance which makes 

 its appearance at a very late period in digestion and in the 

 posterior end of the mesenteron. The effect of the production 

 of this substance is to cause the faeces to change from particles 

 scattered through the lumen to a compact mass which occupies 

 the centre of the gut and is not in contact with the walls. 



This concludes the main part of the paper, and in it we have 

 endeavoured to show that the apparently undifferentiated mes- 

 enteron of Daphnia is really divided into regions defined by 

 the processes which take place in them and by the character of 

 the cells forming their walls. 



In order to complete the account of the histology of the gut 

 we will briefly describe the structure of the stomodseum, procto- 

 dseum, and muscular basement membrane of the mesenteron. 



