48 Development and Shape of Uriniferous Tubules 



species of animals are compared. In human and pig embryos the Mal- 

 pighian corpuscles develop relatively early, when considering the extent 

 of the development of a given uriniferous tubule and may assume a 

 nearly spherical form before the portion of the tubule which forms the 

 anlage of the loop of Henle is clearly differentiated. This, H and I of 

 Fig. 4 may serve to illustrate. On the other hand in cat and rabbit, 

 developing uriniferous tubules are often met with in which the anlage of 

 the loop of Henle is clearly made out, before the Malpighian corpuscles 

 have progressed in development beyond the stage in which they are of 

 hemispherical shape, with the epithelial portion in the form of a double- 

 walled cup, as for instance shown in E of Fig. 5, and F and Q of Fig. 6. 



Attention may yet be called to the fact that Malpighian corpuscles 

 develop in about the location in which they have their anlage. Through- 

 out the period in which new tubules are formed, new generations of 

 tubules and Malpighian corpuscles develop outside (toward the periphery 

 of the kidney) of those previously formed, which makes it appear as 

 though the Malpighian corpuscles of the older generations of uriniferous 

 tubules sank down into the deeper parts of the parenchyma of the kidney 

 as this developed. Herring, who has called especial attention to this 

 fact, expresses himself as follows : " The Malpighian corpuscles seem to 

 be fixed structures at an early period and do not move their position 

 as do the tubules during their further growth. The early fixation seems 

 to be due to the density of the connective tissue around the Malpighian 

 body and it is likely that a certain part always remains constituting the 

 framework." The size of these structures when compared with the other 

 portions of the tubular anlagen, the compactness of the glomerular anlage, 

 when compared with the surrounding mesenchyme, but especially the 

 early development of a definite vascular supply to the glomerulus, all 

 appear to me to form factors which assist in the fixation of the developing 

 Malpighian corpuscle. 



At about the time when the developing Malpighian corpuscles have 

 reached a stage of development in which they resemble in shape and to 

 a certain extent in structure, fully developed Malpighian corpuscles, 

 there is observed a cellular differentiation in that portion of the tubules 

 which we have designated as the anlage of the proximal convoluted 

 portion. Beginning with the region of attachment of this portion of the 

 tubule to the Malpighian corpuscle and proceeding for the remainder 

 of its extent it may be observed that the protoplasm of the epithelial cells 

 increases in quantity and becomes clearer and now takes more readily a 

 protoplasmic stain, so that in sections stained with hrematoxylin and 

 eosin or erythrosin, the protoplasm of the cells appears tinged with red. 



