36 Charles GELDERD 



an infinity of very fine hairs, closely packed together and pointed in an 

 oblique direction upwards, fig. 28. 



At the posterior end of the cavity the grooves in the plates 5, are no 

 longer seen, fig. 29. 



In this région which is close to the opening of the digestive glands, 

 the lower portions of the plates 5^ are turned in at an angle to meet the 

 convex corners of the médian pièce S, just above the hollowed out entrance 

 to the grooves of 5^, fig. 29. 



The small hairs upon the lower surfaces of the plates 5, brush against 

 the angular corners of the médian pièce, so that no food matter can fall 

 into the passages below, which are the channels by which the sécrétions 

 from the glands enter into the latéral grooves of the pièce S,. 



Our préparations show that much alimentary matter is accumulated, 

 in this région of the pyloric cavity above the lower passages. 



Two dorsal diverticula are found in Alacropsis lying side by side above 

 the posterior end of the pyloric chamber, fig. 26, 30. 



Their rounded off summits project towards the cardiac chamber. They 

 open laterally at the beginning of the intestine where the pièces 5^ and 

 PJ^ terminate. 



The digestive glands hâve the same structural plan as that of our 

 type; the ordinary secreting cells arç, however, much longer in places 

 than those of Macromysis Jlexuosa, forming eminences in the lumen of 

 the tube, fig. 47. 



The glandular ridges that we observed in our type are found in the 

 corresponding pairs of tubes, the third dorsal and the ventral pairs. In 

 Macropsis, however, more than one is generally found in the same tube, 

 and they are of a somewhat différent aspect. 



The cells in thèse formations do not stand out prominently in the 

 tube; there is the same process of vacuolisation with the formation of a 

 thick cuticlc and the débris of cell membranes. 



The distinctive différences of structure in Schistomysis ornala, Mysis 

 vulgaris, Schistomysis spiritus, Gastrosacciis spinifer, and Mysidopsis are 

 in the disposition of the dorsal diverticula and the glandular formations of 

 the digestive gland. 



Thèse différences are compared in the following table : 



