Irving Hardesty 337 



rounding it wliicli is apparently more compact and which stains a deeper 

 blue than the protoplasm of the general syncytium, but instead of having 

 a definite outline the protoplasm seems to grade off into that of the 

 syncytium. This condition is apparent in iiber c of Fig. 2. In general, 

 the nuclei of this stage are merely imbedded in the syncytial protoplasm 

 and show the various types of the neuroglia nuclei. 



The appearance of definitely formed seal-ring cells is shown in Fig. 3. 

 In this figure are represented two small areas from transverse sec- 

 tions of the spinal cord of a pig of 21 centimeters stained by the Benda 

 neuroglia method. The cells (c) here show the form suggesting the name 

 given them. Their finely granular protoplasm stains a decidedly deeper 

 blue than that of the now more sparse protoplasm of the general syncyt- 



FiG. 2. From the spinal cord of a pig of 16 centimeters. Osmic acid and 

 fuchsin. Teased by water. rt = axones before medullation; 6=:axones 

 showing beginning medullation; c= fiber in more advanced stage of medul- 

 lation and with probable sheath cell; s = syncytial protoplasm. X 550. 



ium and their boundaries are definite. The fields were chosen because 

 of each having two cells near together, three of the cells containing nuclei 

 in the section. With the nucleus in the thicker side, the cells usually in 

 this stage completely enclasp the fiber as a ring, but sometimes the pro- 

 toplasm on the side away from the nucleus is either absent or so thin 

 as to give the appearance of a crescent. Frequently a cell is found of 

 the shape presented in d, where the protoplasm seems mostly extended 

 from one side. In sections, the cells seldom seem to produce a depres- 

 sion in the medullary sheath for tbe fiber usually appears circular. Very 

 probably none of the fibers possessing these cells are full grown, for the 

 cells are found more abundant at about this age and the average diam- 

 eter of the medullated axones here is much less than that of the adult. At 



