CELLULAR ELEMENTS OF THE MAMMALIAN EMBRYO 95 



ocytically ingested, or originally intra-cellular elements, some 

 of which had been subsequently extruded from the parent cell. 

 The point then to be estabhshed is the correctness of one or 

 the other of these two alternatives. The abundant occurrence 

 of these elements in such tissues as the brain wall and nerve 

 ganglia which are relatively deficient in mesenchymal cells is a 

 fact in itself sufficient to raise a question as to their intra-cellular 

 origin. Again upon examining the bodies in question it will 

 be observed that they may present a variety of structural forms, 

 among which may be noted single small basophilic spherules 

 surrounded by just a trace of eosin staining material (fig. 31a), 

 several basophilic spherules situated in a larger red staining 

 body (fig. 316), a crescent, or less frequently, a spherule of baso- 

 phihc substance peripherally located (figs. 31, c, and d and 32), 

 or a peripheral basophilic ring completely surrounding the red 

 stained material (figs. 31e, 33e, and 28). Now if one turns to 

 the circulating blood of these same embryos, degenerating nu- 

 cleated erythrocytes are occasionally found, as is well known, in 

 which the disintegrating nuclei have become broken up into sev- 

 eral small more or less rounded fragments. Again in other in- 

 stances such degenerating nuclei, especially in the mouse em- 

 bryo, present the appearance of a red stained central area sur- 

 rounded by a peripheral basophilic ring as shown in figures 34a, 

 35 and 36. It may also be observed in the same figures that 

 portions of these rings may be very thin while other areas are 

 much thicker and present the form of basophihc crescents. 

 Similar degenerating nuclear changes can also be demonstrated 

 in phagocytically ingested erythrocytic nuclei as partially shown 

 in figures 4, 6 and 86. Now it is well known and can be readily 

 verified that erythrocytes not infrequently escape from the 

 blood vessels and become isolated in the mesenchymal and other 

 tissue spaces of the embryo where they may undergo various 

 types of disintegration (Minot, '12, p. 509). From the data 

 derived from the erythrocytes occasionally degenerating in the 

 circulating blood it becomes evident that these degenerating 

 corpuscles may assume structural appearances identical in char- 



