426 H. BOSCHMA. 



opened a polyp and noted the changes in the mesenterial filaments 

 and in the copepods. The results were the following. 



Half an hour after the feeding in the digestive zone of the 

 mesenterial filaments a number of red vacuoles are visible. Be- 

 sides these vacuoles which have a fuchsin like hue (acid reaction), 

 the remainder of the mesenterial filament, including the marginal 

 part, has absorbed some neutral red which is unchanged in color. 

 The copepod still has a deep red hue. 



Gradually now the intensity of the color of the mesenterial 

 filaments increases whilst the color (together with the muscles and 

 other soft parts) is extracted from the copepod. At first the 

 parts of the copepod which are lying against the mesenterial fila- 

 ments lose their color, the distal parts of the appendages usually 

 keep the neutral red longer than the central part of the animal. 

 After two hours the mesenterial filaments are strongly colored, 

 whilst the copepod is almost completely devoid of its soft parts 

 and only the bare skeleton is left. 



When the polyps are cut open to study the changes in the food 

 and in the digestive organs the parts of the skeleton of the copepod 

 usually disjoint. To avoid this the experiment can be modified 

 in some respects. When a polyp, including the skeleton, is cut 

 longitudinally into two halves, the digestive function of the 

 mesenterial filaments may be studied under the microscope. The 

 skeleton prevents the tissues from contracting strongly after the 

 dissection and the mesenterial filaments remain clearly visible. 



A copepod vitally stained with neutral red placed on the mesen- 

 terial filaments soon becomes partly enveloped by a few coils of 

 these organs and the struggling movements of the animal soon 

 come to an end. After some time (a quarter of an hour to half an 

 hour) these coils withdraw from the food and then the digestive 

 zone of their surface which has been in contact with the copepod 

 has assumed a red color, thereby forming a striking contrast with 

 the remaining parts of the mesenterial filaments. These colored 

 parts, then apparently saturated with food, slowly bend away 

 from the copepod and other coils of the same or a neighboring 

 mesenterial filament take their place. The copepod remains 

 intact as far as the external form is concerned till almost all of 

 the colored internal tissues have been absorbed by the mesenterial 



