CYTOLOGICAL CHANGES ACCOMPANYING DESICCATION. 335 



of which in the stomach tissue is not constant, is lined with a 

 heavy ciliated cuticula. Just beneath the cuticula are found 

 longitudinal muscle fibers arranged at regular intervals. The 

 part of the stomach outside the thin layer of muscle fibers is 

 syncitial in nature. With the iron-haematoxylin-eosin-lichtgriin 

 stain of de Beauchamp three elements may be distinguished, (i) 

 nuclei having, in general, the same structure as those described 

 for the vitellarium; (2) densely staining granules of great size, 

 not surrounded by a clear area or membrane. These are prob- 

 ably aggregations of food material. (3) Vacuoles of greater or 

 less size which stain with lichtgriin. These last are probably 

 globules of excretory material as de Beauchamp has pointed out. 

 In the latter's description of the stomach of Callidina socialis 

 he says that the stomach is not surrounded by an "individualized 

 membrane" but only by a layer of protoplasm which projects 

 at the periphery. In P. roseola, as far as I have been able to 

 determine, a true membrane is present (Fig. i). 



The skin of P. roseola has practically the same structure as 

 that of other rotifers. It consists of two layers, cuticula and 

 hypodermis. The former is the more densely staining layer and 

 is composed of fine granules closely packed together; the latter 

 is a finely reticulated plasma layer in which cell boundaries 

 cannot be distinguished and in which nuclei are found scattered 

 at irregular intervals. The skin is pliable and may be readily 

 folded at any point. It is difficult to obtain sections in which 

 one or more of these folds do not appear. 



The brain of P. roseola is of an elongated triangular shape and 

 lies in front of and slightly above the mastax. Zelinka ('88), 

 in the case of Discopus synaptce, has figured the brain as a synci- 

 tium in which the nuclei are closely packed together about the 

 periphery, while in the central part is found the " punk stubs tanz," 

 a finely granular portion without nuclei. In the greater number 

 of cases I have been able to distinguish definite cell boundaries 

 in the case of the cells forming the peripheral layer of the brain 

 of P. roseola. The nuclei of these cells are uniformly circular 

 in section and contain a small amount of chromatin scattered in 

 irregular masses through a homogeneous nuclear plasm. The 

 cytoplasm is homogeneous and has the appearance of a colorless 



