DESICCATION IN PHILODINA ROSEOLA. 359 



walls of the pharynx with their internal ciliation are not markedly 

 different in the two forms. 



A section through the esophagus is shown in Fig. 8, Plate III. 

 As was mentioned before, the esophagus is difficult to observe 

 in the living animal because it is generally concealed by the 

 salivary glands which surround it. The section shows it to be a 

 narrow, thin-walled tube. Surrounding it are the salivary 

 glands whose cytoplasm is uniformly granular but not divided 

 into distinct cells. The nuclei appear scattered irregularly and 

 have the characteristic structure found in like elements of other 

 tissues. 



The esophagus in section in Discopus shows about the same 

 relative size and position as it does in Philodina. It is likewise 

 surrounded by the salivary glands so that it probably is not 

 visible in the living animal. The salivary glands of Discopus 

 do not appear to be as dense or deeply staining as those of 

 Philodina. The cytoplasmic granules are less closely packed 

 together and the nuclei appear to be less chromatic. The most 

 noticeable difference between the figures of sections of corre- 

 sponding regions in the two animals is the lack of hypodermal 

 tissue in Discopus. While it is to be expected that the integu- 

 mentary structures would be thinnest at the points of greatest 

 flexibility, it seems that the total absence of hypodermis in this 

 and some other of Zelinka's figures must have been a result of an 

 oversight on his part. 



A section through the middle portion of the trunk (Fig. 9, 

 Plate III.) shows the reproductive glands and the middle portion 

 of the digestive system surrounded by a somewhat thicker ring 

 of the integument. The plasma of the vitellarium is a syncytium 

 made up of granules of varying sizes. The granules are sur- 

 rounded by small, clear areas containing a cell-sap which is lost 

 during desiccation. The nuclei of the vitellaria (v) are the 

 largest to be found in the rotifer body. These consist of a single 

 karyosome surrounded by a clear homogeneous area and having 

 at the periphery a distinct nuclear membrane. This is the 

 "nucleolar nucleus" of Carnoy and is characteristic of most of 

 the cells of the rotifer tissues. The ovary (ov) is a small elon- 

 gated structure lying in a depression of the inner border of the 



