336 LOUIS M. HICKERNELL. * 



fluid. The " punktsubstanz" lies approximately at the center of 

 the organ and is granular in structure. 



In the fully extended living Philodina the ciliated or trochal 

 discs are prominent at the anterior end of the body. The cilia 

 upon these discs by their successive beating give the effect of a 

 revolving wheel. When the animal is disturbed the discs are 

 folded and retracted into the pharyngeal region where they may 

 be observed as oval patches. The alimentary canal is also 

 ciliated throughout almost its entire length. 



Of the glandular structures, other than those employed for 

 reproduction, the slime glands of the foot are perhaps most easily 

 seen. These consist of rows of cells whose cytoplasm is alveolar 

 or finely reticular. The nuclei are large and may sometimes be 

 seen in the living animal. The digestive glands in the region 

 of the mastax are similar to the foot glands in structure and 

 staining qualities. 



The changes in cell organization which accompany the process 

 of desiccation are fairly uniform in result for all the tissues. 

 Although slight variations have been observed, these are dif- 

 ferences of degree and not of kind. Since the cellular elements 

 are larger and hence more easy to observe in the vitellarium, 

 this organ will be considered first. 



In a section of the vitellarium of a desiccated P. roseola the 

 most noticeable difference from the conditions which are present 

 in the normal tissues are seen in the nucleus. Normally, as was 

 stated before, the nuclear membrane, though definite, is not 

 very thick. Just within the membrane is a ring of homogeneous 

 ground substance or nuclear sap. In the center of the nucleus 

 is found the large, densely staining karyosome. In the dried 

 animal these conditions are exactly reversed. The karyosome 

 may disappear entirely but if this extreme condition does not 

 come about, the structure which remains in the position of the 

 karyosome is similar neither in shape nor in staining qualities 

 to the original element. In extreme cases the central area of 

 the nucleus in the dried organ has exactly the same appearance 

 as the clear area of the normal nucleus. The nuclear membrane 

 becomes heavy and has the appearance of a thick ring (Fig. 5). 

 In most cases it appears to be composed of fine granules closely 



