RESEARCH ON THE DIGESTIVE SYSTEM OF THE SCHIZOPODA 31 



The long tubes of the digestive gland contain two différent kinds of 

 cells, FiG. 45, 46. 



If one of the long tubes be sectioned transversely, either the third 

 dorsal or ventral, at some distance from the common duct, besides the 

 ordinary secreting cells a very singular glandular ridge is observed in the 

 lumen of the tube, which as far as we know, has not yet been seen or at 

 least described by any previous author, fig. 45, 46. 



It consists of a semi-ciicular mass of elongated cells, in a transverse 

 section. Regarded in a horizontal section, it is seen to run as an irregular 

 ridge standing out prominently in the lumen of the tube, fig. 46. 



The cells of this strange formation undergo a process of vacuolisation 

 leaving a scaffolding of cell membranes which support a roof-like cuticle, 

 fig. 45, 50. 



In the horizontal section it will be seen that at the extremity nearest 

 to the opening of the digestive glands into the stomach, the vacuolisation 

 is complète, fig. 46, 



There is always found, however, at the basai part of the cell mem- 

 branes a small amount of protoplasm with a small nucleus. 



In a transverse section this ridge has a fan-like appearance, fig. 45. 



We shall give a detailed description of this glandular ridge in our 

 histological chapter; hère we shall only indicate where it is found. 



In following a séries of transverse sections through one of the long 

 tubes, beginning at their extremity, after a short distance we encounter 

 a small semi-circular mass of cells somewhat longer than the others and 

 with a slight différent nucleus. 



They are closely packed side by side. 



As we advance towards the stomach they gradually increase in lengttr" 

 till at a certain point they decrease again, fig. 46. 



The progress of the process of vacuolisation advances as we near the 

 stortiach, fig. 46. 



It first makes its appearance near the extremity of the tubes just be- 

 neath the membrane of the cells. 



This glandular ridge is found only in the pairs of long tubes in Macro- 

 mysis flexuosa. 



The shorter tubes contain only the ordinary secreting cells, fig. 49. 



In our type there is only one glandular ridge in each tube, and they 

 are placed back to back so that a transverse section of the pair of tubes 

 gives the two glandular ridges a butterfly appearance. 



