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spindle cell. Focusing on the surface of the nucleus will usually satisfy 

 the observer that he is looking into a groove, and an examination of 

 optical sections, such as is seen on the right of figure 6, gives con- 

 vincing proof of this. Eeference to Werzberg's own figure (fig. 14, 

 plate V) shows clearly that his " parachromatin canals" are merely 

 indentations of the surface which are filled with cytoplasm. Further 

 evidence for this is the fact, that the "canals" are always filled with 

 a substance which is identical in its staining reactions with the sur- 

 rounding cytoplasm (figs. 4 and 14 of Werzberg's paper). The longitu- 

 dinal strands of chromatin are, therefore, not real structures, but are 

 optical appearances produced by the irregularities of the surface 

 of the nucleus. These grooves or folds are usally in the long axis of 

 the nucleus, but they may take any other direction. There may be 

 several grooves on the surface of a nucleus, and several of them may 

 run together in such a way that one groove will appear to break up 

 into several branches. The grooves may be confined entirely to the 

 more flattened surfaces of the nucleus, or one or more of them may 

 run around the end of nucleus and cut into it so deeply that this end 

 appears lobulated (fig. 6). 



Within the nucleus the chromatin is disposed in coarse irregular 

 masses. It is very abundant, but never forms longitudinal bands, as 

 described by Werzbbrg. With Eomanowsky stains there is no evi- 

 dence for the presence of ,, Parachromatin" between the masses of 

 chromatin. 



Erythrocytes. 

 The erythrocytes of Amblystoma, when compared with those of a 

 reptile, are interesting from the standpoint of Minot's theory, that 

 the erythrocytes of the Ichthyopsidae have a nucleus which contains 

 an open chromatin network or distinct chromatin granules, in contrast 

 to that of the Sauropsidae which is dense and pyknotic and shows no 

 chromatin structure. According to Minot, the first form of nucleus, 

 which is permanent for the Ichthyopsidae, corresponds to that of the 

 so-called 'erythro blast' of mammals, while the second form is similar 

 to the nucleus of the mammalian 'normoblast'. Since Minot believes 

 that the latter is the permanent form of nucleus for the erythrocytes 

 of the Sauropsidae he proposes to substitute the term "sauroid" cell 

 for 'normoblast' in the mammals, and "ichthyoid" blood cell for 

 'erythroblast'. 



